Description of problem:

Bug appears in:

• Technology Preview of gimp 2.99.8 in RHEL9
• Built versions of gimp 2.99.16 and nightly from copr on Fedora:
  https://copr.fedorainfracloud.org/coprs/uriesk/gimp-nightly (spec file is an updated version of the one from RHEL)

When i hover over an item in the toolbar for a second, just when the tooltip is supposed to appear, the highlight of it starts to flicker instead. If I hover over an entry in the menu or a dropdown that das a tooltip, the selection will flicker.
This does not happen on every single tooltip, i.e. all the tooltips in the Test -> Testdialog work fine.

How reproducible:

Steps to Reproduce:
1. Install gimp technology preview on RHEL or gimp-2.99 from copr on Fedora (URL above)
2. Hover over a button in the toolbar or an menu item that has a tooltip

Actual results:

More likely then not, the selection / highlight will start to flicker and no tooltip appears.

Expected results:

Tooltip appears and no flickering.

Additional info:

Upstream bugreport: https://gitlab.gnome.org/GNOME/gimp/-/issues/9795