artifact outline when wine window is behind active window

[naftahorn]

Linuxmint 19.3, winehq-staging v5.8 on kernel 5.3.0-51-generic

wine program that is the culprit is "PDF-XChange Editor" v8.0.331.0

What I notice is that while I have this program running, it is not minimized, and is behind other windows, i notice it's outline as per attached images:

screenshot_wine_artifact_pdfxchange-2.jpg (12.99 KiB) Viewed 722 times

screenshot_wine_artifact_pdfxchange-1.jpg (2.72 KiB) Viewed 722 times

Notice the faint black outline that shows within the infront window, and that when i mouse over this outline i can grab it; allowing me to interact with PDF-XChange even while it's behind the active window.

I suspect this is probably a problem within PDF-XChange as I can't find a winecfg setting that will make it go away. Therefore am posting here in the hopes that a more knowledgeable person can give aid? Note, I have noticed that in using PDF-XChange v6 this isn't a problem. I'm not keen on using v6 though, as there are key features in the later version that I really like. Hence this post.