I cannot explain EXACTLY why.
However I can hazard a pretty fair bet that the older (very very old) version had more compatibility with earlier versions of windows and that an updated (newer) module to ease use in newer OS ignored the requirements it no longer needs.
I just fired up 1.6.5 and that comes up OVER file explorer (1.6.5 was a very stable release btw).
It seems this is a change from 1.8.? onward.
Reason I don't seem to notice is that I run two screens.
You might have found an obscure bug.
Maybe you should go to GitHub and open an issue there where the developers frequent more often ?
Bob.