versions of Windows you are using where this happens
Windows 10 [Version 10.0.19043.928]
As far as I know, this the first time this issue has been reported since the feature was added in 2021.
issue has existed since at least 7.73-7.74 that i have noticed (probably since the new mdis were introduced), and as you see it took me this long to report it. i have not tested 7.81, but it does exist on versions up to and including 7.79.
Is it possible that this may be related to something specific about your Windows configuration?
certainly this can be, however it does happen on multiple computers with non-identical setups.
but sadly this does not really help with troubleshooting this.
configuration is reasonably standard, no huge changes that should cause this that i can think of.
if i am correct and this is custom theming/handling/etc of mdis, perhaps the easiest solution is to add an option to disable that and use the standard vista-like mdis. this should solve the problem (and i suppose some people will prefer the vista look over modern).