HeidiSQL 9.3.0.5051 OS: Windows 10 I'm using built in Windows feature - virtual desktop (pressing Win+Tab you can create a new Desktop). Then open up HeidiSQL and have an autocomplete window opened (does not matter how, select * from + ctrl+space will do). Dismiss the autocomplete window. Now if you switch between virtual desktops with shortcut Ctrl+Win+Arrow-Right, the autocomplete window will be opened again on the wrong desktop. And it cannot be closed until you identify from which heidisql window (if you have more than one open) it came from. Only when you open up the window in question the autocomplete popup will disappear. The only workaround I found out was to use Win+Tab when switching between desktops. It does not open the autocomplete popup that way. Still very annoying...
In the attached screenshot you can see the autocomplete popup open while I'm browsing heidisql forum from firefox.