Unfortunately, I do not have a single exact reproduce case that can force the behavior on demand.
Sometimes it happens while I'm typing.
Sometimes it happens while I'm selecting text.
Sometimes it happens while my hands are off the keyboard.
It happens with all the file types I have edited so far (cpp, c, java, xml).
It doesn't happen at regular intervals.
If I have a single editor window maximized I get the bar to block cursor and can't type.
If I have multiple editor windows visible I can see the window border change colors and lose focus as the cursor changes.
It's only the editor window. I don't have focus problems with other windows.
The focus always comes back to the editor window if I stop and wait about 5-10 seconds. In the meantime, any keystroke just beeps as if nothing has focus (i.e. I can't see any other form/control that has focus). Obviously I can force it back by clicking the mouse in the editor window or using Atl+Tab to refocus the app.
I posted here because I don't have an explicit on-demand reproducible case - hoping someone else might have figure it out or at least could help in further diagnostics.