Genre - incorrect/empty images

[Alcyone7 10]

I have two libraries: TV Shows and Movies, both set to their appropriate library type. 

In the Movies library, when I go to Genre - the images shown in the main window include covers from what are clearly TV Shows, and the same for the genre menu in the TV Shows, with lots of movie covers.  Is this normal?

When I click on the respective genre categories, they show TV Shows only / Movies only as I would expect, and do no include the errant entries shown in the genre category thumbnail. I have deleted the images, told it to re-scan the artwork - and the same thing - artwork from a totally different library is included.

I have taken a quick look at the DB and I have found movies showing as:

"isinmixedfolder=0"

as expected... but the TV Shows, the containers are fine, but the individual episodes show:

"isinmixedfolder=1"

I am concluding that "isinmixedfolder" simply denotes that the folder contains different video files, not different versions of the same content... so fairly sure this is not behind the weird thumbnail generation of genres for the two different libraries being "mixed" up.

Are the thumbnails being mixed by design, or is this a potential bug?  
Emby Server: v4.9.5.0