Thanks for explanation. However, I am not still sure what the issue is. You wrote:
When activating Window#2, pressing Ctrl+F||Ctrl+H opens a dialog (briefly) then it seems to go off the desktop – disappears.
This alone is quite strange. Does the Find (or Replace?) dialog box briefly appears and then disappears?
Can you disable all plug-ins and try again?
Maybe a screencast might be more helpful.
I am sorry for any inconveniences.