Weird extra "window within windon" in SQL panel

If I write some MYSQL code to manually run a query, more often than not a kind of "mini-window frame" appears over the text after the query is run, which seems to be sized about 6 rows high and about 20 characters wide. The frames of that window obscure the text.
I can move text down to see the part covered by the frame so it is not actually "in" the query window but "over" it. If it is a very simple query then the ghost window is less likely to appear but for more complex ones it usually does. I have attached a screen shot using a really awful colour which shows it very clearly (not a colour scheme I would otherwise recommend). I run on Windows10 64 bit with HeidiSQL build 10.1.0.5479 The problem has existed for a while - I keep hoping that by running the nightly build it might be fixed.

Sorry - title should read "Window within window"