K-Meleon 75.1 browser from rapps, impossible to select anything from drop down menu

0.4.9-RC-32-gfb0fd2b gcc dbg on VBox 4.3.40 (without additions)

K-Meleon 75.1 browser from rapps (the app is inconsistent in naming its version, at some places it still states K-Meleon 75.0)

There is a button to open the settings menu.
When you press it a drop-down-menu opens up.

Observed result
But very quickly it gets covered by another menu which effectively prevents you from ever accessing the first menu.(and all of its functionality).
0.4.9-RC-32-gfb0fd2b_vs_KMeleon.webm
kmeleon.log logs only the last unrelated alphablend lines then.
I noted this issue for each rls test since ros 0.4.1rls already, so it's nothing new.

Expected result
xpsp3_ok.webm