I could not agree more. I have found a screen goes gray when the
processor is doing the task the window is open for, but there is more.

If a popup window is opened by the window in question that expects a
response the window can also go gray. The tray may show a tab for a
window that may have opened up under rather than on top of the window
that opened it. If this happens the machine seems to be locked up but
it isn't.

Use the tab on the tray to bring into focus any windows under the window
that is gray. The only one that will come into focus is the popup
(dialog box) that needs an answer.

I may be wrong but that is what happens to me on occasion, when I act to
quickly.