How to fix blank/default icons on Windows 7 Task Bar (oops!)

My office is in the process of converting from Windows XP to Windows 7 and I am one of the early testers.  One problem I ran into was that Acrobat PDF files would open-up but without the proper Acrobat icon on the Task Bar.  Normally you could simply right-click on the Task Bar icon, then right-click again on the program name ("Adobe Acrobat') and then click on 'Change Icon' to fix it.  But because of the way Acrobat installed the 'Change Icon' link was greyed-out.

When I tried googling this situation I found lots of varied suggestions, none of which seemed to apply.  What seems to have worked, fortunately, was the following procedure which I believe triggered an update/refresh of the cached icon-image for Acrobat.

PROCEDURE

1. located original 'acrobat.exe' in C:\Program Files\Adobe\Acrobat 9.0\Acrobat
   (I noted that it had the correct icon but it was missing from Task Bar once opened)
2. created a shortcut to the .EXE
   (the shortcut also had the correct icon)
3. opening the shortcut showed the correct icon!  
4. At this point I temporarily pinned the app to the Task Bar.
5. I tried opening some PDFs and found that they opened in the pinned app and with the correct icon
6. I unpinned the app from the Task Bar
7. I opened some PDFs again and now the icon is correct

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UPDATE: And just like that it's gone...  I thought I had fixed it this morning but now it's broken again.