ScreenUpdating=False fails to prevent screen updating, and causes bizarre behaviour

Question

I have recently installed Office 2013 (MSO Standard 2013) on my (Win 7 Professional) computer.  During a brief transitional period, Office 2003 will remain on my computer.
I had been looking forward to running the many Excel VBA applications on Excel 2013, but am not only disappointed, but alarmed.  We are significantly dependent on over 50 business applications running in Excel VBA (many of which are complex,
and many of which I have developed), but we now find that seemingly one difference alone (though we may yet discover more) is rendering many of them virtually unusable.  That difference is the behaviour of the Application.ScreenUpdating method.
In Excel 2003, the ScreenUpdating method behaved intuitively, predictably and reliably.  It basically does what it says - all screen updating, except for the status bar, is frozen.  To allow users to peek at any updates, one would simply
set ScreenUpdating=True and at the appropriate point freeze updating with ScreenUpdating=False.  Now, in Excel 2013, we are instead finding behaviour which has to be described as bizarre, counterintuitive and destructive.  Essentially, what is happening
is that whenever another worksheet is activated, ScreenUpdating=False does not prevent screen updating - and for good measure, there are a number of other unpleasant side-effects.  I have spent many long hours searching through hundreds of forum posts
and testing workarounds - all without success.  I have seen many posts complaining about ScreenUpdating in Excel 2013, but not a single implementable solution.  Yes, I've seen the advice about replacing Select or Activate methods with objects, but
this workaround would not only be extremely costly and impractical in our case (it would require reworking tens of thousands of lines of code and would probably take many person months of unjustifiable work), it almost certainly wouldn't work.  (You'll
have to take my word on that.)  And all because ScreenUpdating=False doesn't really prevent screen updating any more!  I cannot accept that ScreenUpdating is working properly in Excel 2013, nor that its functionality is in any way acceptable.
The problems are best illustrated with a simple example.  I created this example to verify that the flickering was unrelated to the complexity of the business applications I referred to above.  In this example, there is a "master"
workbook named "ScreenUpdatingTest.xls".  This contains a single button on its only worksheet, and this button executes macro "TestScreenUpdating".  This macro turns screen updating off, then sequentially opens workbook AAA.xls,
workbook BBB.xls and workbook CCC.xls with a 3 second interval between each workbook being opened.  After 3 more seconds, it activates workbook ScreenUpdatingTest.xls and then turns screen updating on.  Along the way, it reports these actions in
the status bar.  One would expect that this would result in AAA, BBB and CCC being opened in the background, with the user seeing no changes on the screen apart from the status bar and the workbooks appearing in the task bar.  This is precisely what
happens in Excel 2003.
By contrast, Excel 2013 seems to do absolutely nothing for about 12 seconds (even the task bar and the status bar remains unchanged), then, AAA, BBB and CCC can be seen to open (in maximized windows) in rapid succession.  The only message I see in the
status bar is the last one, "Switched back to ScreenUpdatingTest.xls."  Even more bizarrely, that there is a call to Msgbox "Hi" just before the Application.ScreenUpdating=True at the end of the subroutine - and this should be unrelated
to which workbook the focus end up with, right?  Wrong!  If Msgbox "Hi" is commented out, the focus ends up with CCC.xls - in other words, Workbooks(ThisWorkbook.Name).Activate seems to be ignored.  But if Msgbox "Hi" is
uncommented, the focus ends up with ScreenUpdatingTest.xls!  This is crazy, isn't it?
Sub TestScreenUpdating()
Application.ScreenUpdating = False
Application.Wait Now() + TimeValue("00:00:03")
Workbooks.Open ThisWorkbook.Path & "\AAA.xls"
Windows("AAA.xls").Activate
Application.StatusBar = "AAA.xls has been opened."
'Excel 2003:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls is open in the task bar.
' The message that AAA.xls has been opened appears in the status bar.
'Excel 2013:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls is >>>NOT<<< open in the task bar
' >>>NO<<< message that AAA.xls has been opened appears in the status bar.
Application.Wait Now() + TimeValue("00:00:03")
Workbooks.Open ThisWorkbook.Path & "\BBB.xls"
Windows("BBB.xls").Activate
Application.StatusBar = "BBB.xls has been opened."
'Excel 2003:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls and BBB.xls are open in the task bar.
' The message that BBB.xls has been opened appears in the status bar.
'Excel 2013:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls and BBB.xls are >>>NOT<<< open in the task bar.
' >>>NO<<< message that BBB.xls has been opened appears in the status bar.
Application.Wait Now() + TimeValue("00:00:03")
Workbooks.Open ThisWorkbook.Path & "\CCC.xls"
Windows("CCC.xls").Activate
Application.StatusBar = "CCC.xls has been opened."
'Excel 2003:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls, BBB.xls and CCC.xls are open in the task bar.
' The message that CCC.xls has been opened appears in the status bar.
'Excel 2013:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls, BBB.xls and CCC.xls are >>>NOT<<< open in the task bar.
' >>>NO<<< message that CCC.xls has been opened appears in the status bar.
Application.Wait Now() + TimeValue("00:00:03")
Workbooks(ThisWorkbook.Name).Activate
Application.StatusBar = "Switched back to ScreenUpdatingTest.xls."
MsgBox "Hi"
Application.ScreenUpdating = True
'Excel 2003:
' I see workbook ScreenUpdatingTest.xls on the screen with no flickering.
' AAA.xls, BBB.xls and CCC.xls are open in the task bar.
' The message that we have switched back to ScreenUpdatingTest.xls appears in the status bar.
'Excel 2013:
' Workbooks AAA.xls, BBB.xls and CCC.xls appear in rapid succession.
' When execution ends:
' If Msgbox "Hi" is commented out, the focus is with CCC.xls.
' If Msgbox "Hi" is uncommented, the focus is with ScreenUpdatingTest.xls.
' AAA.xls, BBB.xls and CCC.xls are >>>NOT<<< open in the task bar.
' The message that we have switched back to ScreenUpdatingTest.xls appears in the status bar.
End Sub
Surely it is reasonable to expect that such functionality should remain consistent from one version to the next!  Our applications in Excel 2003 had a professional, elegant user interface, and they behaved predictably, intuitively and robustly. 
With Excel 2013, this is utterly trashed, with flickering, unpredictable behaviour (who knows what will get the focus?) and inefficiency (things are so much slower when the screen updates).  With Office 2003 going out of support, vast numbers of people
in my company will be moving to Excel 2013 as Excel 2003 is decommissioned.  I imagine the same will be happening in many other companies.  We now find ourselves on the cusp of being dealt us a devastating blow due to ONE DYSFUNCTIONAL METHOD, and
we are desperate for a solution.  A solution would either have to restore the former Excel 2003 functionality of ScreenUpdating, or it would have to introduce a new method which really does turn screen updating on or off without exception.
Please, HELP!
-Peter

Answer 1

Thanks for the input, Jim.
I don't think the Single Document Interface is contributing to the problem.  Since installing Office 2013, Excel 2003 has also inherited a Single Document Interface - yet while it behaves like a charm, Excel 2013 behaves ineptly.
Whatever the reasons for the problem, the fact is that this functionality is now broken - one might even say catastrophically broken - and some sort of resolution is essential.  It would be madness to allow something like this to have such a severe
impact on business operations.
My call for help is still out there, as loud as ever!  BTW, I can send my example files, zipped, to anyone who might like to look at them.
Peter
Sydney, Australia