Eg. gtk+ alters the modality after mapping and
before unmapping the window.
Therfore the former implementation ahd a wrong idea
about the modality until the window was activated and
again had a wrong idea when the dialog closed, keeping
the main client dimmed.
Modality changes at runtime are uncommon but legal and can
happen anytime.
BUG: 321340
FIXED-IN: 4.11
REVIEW: 111154