File Created time changes when file renamed to previously used name

Question

Any ideas on this one would be very gratefully received:
I am trying to rename a file then create a new one with the original name, as part of a solution to roll over log files after x days. 
I found that the new file had the 'created time' of the original file, which messed up the logic badly. I tried to unpick this by creating the new file with a new name, then renaming it. The new file got the correct created time initially,
but as soon as I renamed it to the original name, the created time reverted to the created time of the earlier file.
I even tried simply deleting the old file altogether, but every attempt to get a new file with the original name resulted in the created time being that of the old file.
I have used different filesystemobject instantiations for the old and new files, and I even tried creating the new file in a different run of the script, and in a different cmd session. The only thing that worked was logging out and in again before
creating the new file!
Since the created time attribute is not writeable, I'm struggling to get round this.
Here is a stripped out version that demonstrates it. I have put 5 second waits in, so you can watch the created time get reset in front of your eyes when the new file gets renamed to the old name (might need to add a column for 'created time' to Windows
Explorer)
(OS is 2008 server R2 Enterprise)
$logdir = ".\"
$logfname = "roll.log"
$RollAtDays = 0 # for testing - so it always creates a new file
If ( -not ( test-path $logdir) ){ $newdir = New-Item $logdir -type directory } 
$logfile = $logdir+$logfname
$newlog = $logdir+$logfname+".new"
$fso = New-Object -comobject Scripting.FileSystemObject
$date = Get-Date
# if file exists, test whether it requires rolling over
If ( test-path $logfile ){
 $fo = $fso.GetFile( $logfile ) 
 $dc = $fo.DateCreated
 $RollDate = $dc.AddDays( $RollAtDays )
 # write-host "$dc $RollDate"
 If( $RollDate.CompareTo( $date ) -lt 0 ){
  write-host "Roll"
  $newPath = "$logdir$date-$logfname"
  $newPath = $newPath.Replace("/", "")
  $newPath = $newPath.Replace(" ", "-")
  $newPath = $newPath.Replace(":", "")
  $fo.Move( $newPath )
  #$fo.Delete( ) #tried both renaming and deleting the original file
  start-sleep -s 5
# some code to create a file if one doesn't exist
If ( -not ( test-path $logfile) ){
 $header = "Date"
 $fso1 = New-Object -comobject Scripting.FileSystemObject
 $ts1 = $fso1.CreateTextFile( $newlog, $True )
 $ts1.close()
 start-sleep -s 5
 $fo1 = $fso1.GetFile( $newlog ) 
 $fo1.Move( $logfile )  # this is where the created date gets changed back
 #add-content $logfile $header
# some code to add a line to the log
[string]$logline = "$date"
#add-content $logfile $logline

Answer 1

I have to disagree with the assessment that creation time is not writable:
Get-Item test1.txt | select creationtime
(Get-Item test1.txt).CreationTime = '07/03/2014'
Get-Item test1.txt | select creationtime
CreationTime
3/20/2014 1:15:43 PM
7/3/2014 12:00:00 AM
[string](0..33|%{[char][int](46+("686552495351636652556262185355647068516270555358646562655775 0645570").substring(($_*2),2))})-replace " "