That would be the transient window focus policy wouldn’t it?
My config has:
after setting the focus policy, so transients won’t grab focus - I can see that causing trouble, so you probably just fixed a bug in my config. Thanks.
from the fvwm man page:
The old GrabFocus style is equivalent to using FPGrabFocus + FPReleaseFocus. The old GrabFocusTransient style is equivalent to using FPGrabFocusTransient + FPReleaseFocusTransient.
back on topic - just a wallpaper change:
switched from nitrogen to feh for setting wallpaper- worked out pretty well, feh has some nice options.