I saw your previous post, but didn't think it warranted a response, because you were warning users what to watch out for when running Stardock's WindowBlinds, which modifies the OS.
Well I just wanted to make sure that developers knew that users of their solutions could run into a problem here. Also, WindowBlinds doesn't modify any system files, so it actually doesn't modify the OS.
Talking to a friend who has been a FMP developer for many years, he says this was a problem for Custom Dialogs under Windows (withouut Stardock's WindowBlinds installed) for a long time until it was fixed. Apparently WindowBlinds brings the Close button back, when configured as noted in the first message of this thread.
For what it's worth, Troi Dialog Plugin also shows the Close button, but it remains inactive.