Yosemite keeps forgetting my window arrangement

Question

I'm running OS X Yosemite, 10.10.2 on a:
MacBook Pro (Retina, 15-inch, Mid 2014)
Processor 2.2 GHz Intel Core i7
Memory 16 GB 1600 MHz DDR3
I have an extra monitor plugged into the laptop via a thunderbolt adaptor, and I've set the windows arrangement so that the monitor is above the laptop.
Every time I restart or turn off my Macbook, it forgets this setting and places the monitor to the left of the laptop.
Is there any way I can get it to remember this setting?
I've already tried a couple of solutions I found online for OS X Mavericks that involved clearing or deleting the window settings plist file under
Finder -> Go -> Library -> Preferences -> ByHost, but to no avail.

Answer 1

Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen. Click the Clear Display icon in the toolbar. Then take one of the actions that you're having trouble with. Select any messages that appear in the Console window. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
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