Quote Originally Posted by Krool View Post
The issue with the black line appears to be the DrawThemeParentBackground and the WM_PRINTCLIENT handler.
So, either I remove the WM_PRINTCLIENT handler or remove the DrawThemeParentBackground.

Since it makes maybe sense for "transparent" BP_GROUPBOX style windows to use DrawThemeParentBackground it makes definitely no sense for the FrameW control which is isolated in a UserControl with a fixed BackColor.
The "Transparent" property of the FrameW can be used to draw a fake replica of the parent background already. So there is no need here for DrawThemeParentBackground.

Update released. Fixed. Thanks for reporting !
Really great!
Thank you so much