nanogui: Thread: FLTK Overlay Window does not work with nano-X

I do not have much information yet but there is a bug similar to the one in SetClip.c in nxlib-0.45 that I already found and patched.
What happens is that the FLTK tries to save the area under the window and than restore it when window disappears.
This is different from normal process when the widgets are told to redraw the information under the window.

What happens is that I have a window near the middle of the screen but the area is copied from the upper left corner (origin 0,0).
Looks like there is a sequence of steps and the window coordinates are switched back and forth.
I can see it blink the proper window at the right place but then it is overwritten with wrong data and also I can see the right data shown at the 0,0 for a moment.

My guess is that some pixmap routine in nxlib is not using the coordinates properly or the sequence of commands throws it back to 0,0.

I just wanted to start a thread on this and any suggestions are welcome.
I will continue debugging.

Martin