Mail editor bug when MOVING selected (html) text. (1) It is “clipped” and (2) a remnant lingers on top of the Windows 8.1 desktop and on top of any open app, even after eMClient is closed, usually until the computer is rebooted (sometimes another app will cause it to fiinally diappear)…
The suggestion for other people with the same issue was to make sure they’ve installed the latest version of Microsoft Internet Explorer and the latest version of the drivers for their graphical card.
Does that also help you?
Unfortunately this will most likely not help, I have asked about it and it is clearly caused by IE and even newest version does not help.
Sadly eM Client depends on IE to show emails so that is why this issue is not possible to solve at this moment.