I've noticed this for a while, and should have mentioned it before, but better late than never :)
If there is no editing caret in a window, and Select All is selected in Edit, nothing is highlighted until you click in the editor, whereupon the text is highlighted and then unhighlighted.
Mmmm...It didn't do that with me... :|
Could be another x64 glitch...
For information, I'm with 32 bits XP Media Center 2005, Canada French version.