Often two, and I think sometimes more, windows are shown with active-window highlighting (borders and caption font) when WindowBlinds is active. It is hard to know which window is active, and so I have to click around on the windows. When I do this, the window I click will become active and the others will then show inactive-window highlighting. The multiple-active-window marking occurs sometimes when new windows are created and sometimes when alt-tabbing between existing windows. Sometimes when alt-tabbing, even worse, the window which actually is active is shown with inactive-window marking. Have no definite way to reproduce this reliably.
Don't really need a solution -- it is just an annoyance -- but possibly the developer(s) might be sensitized to this problem.
Windows 10 with current WindowBlinds (Windows 10 Pro 20H2 (19041.vb_release.191206-1406) WindowBlinds 10.89 (064 - Windows 10 Edition) - 64 bit OS)