When using Flight check for the first time on a document, it pops up without a problem.
But when you start looking at your problems and trying to solve them one by one, you can't get back to flight check as it has disappeared.
This can be confusing to new users who 'lose' flight check and don't know where it has gone (taken flight ha ha ha)
The problem is that there is no 'stay on top' command and it has gone behind the main window and so you have to reduce INFIX main window size so that you can see flight check just to click on 'next problem'
This means that the working window is smaller than it should be.
We noticed this problem a couple of weeks ago. It is now fixed and the fix will be included in the next point release of Infix.