> 1. When trying to resize the child frame, adjust_frame_size (...) *is*
 > hit. "configureEvent = ..." is not hit.

OK.  Someone else swallows our resize request and I have no idea who and
why.  Can you try these steps once more with xterm.diff applied?  I'll
attach it again.

 > 2. When moving the child frame by dragging the mode-line (or any other
 > way), the second breakpoint is hit.

OK.

 > The first one (if (FRAME_WINDOW_P (f)) ...), -- isn't hit when
 >  dragging the mode-line. It *is* hit if I call set-frame-position
 >  explicitly from Lisp.

The former uses frame parameters so this is expected.

martin