Currently, the UX skin handles the caption buttons in different ways depending on OS.
For Windows 10, we’ve already had to implement our own buttons. For Windows Vista and 7, we have a decent solution cutting out the caption buttons and letting DWM handle it. On Windows 8, this still works but looks odd (especially with the 7/Vista cutout when using personas, since the Win 8 caption buttons are shaped differently).
A proper solution (with the only drawback being the “out of window glow” not being present on aero glass) would be to always draw our own buttons using XUL, and never use the DWM buttons. This avoids a good number of problems, not in the least issues where these buttons may come up black, being drawn with a delay, or not being drawn at all.
Once this is done, it’ll also become possible to move to always using active layers for accelerated layers which avoids more rendering quirks that are currently present.