UI rendering freezes require focus shift

[threedeyes]

After the latest update (from 254755c to 15c3d4b), the UI occasionally freezes and stops updating. Switching focus to another window and back is the only known workaround to force the UI to refresh and continue rendering.

https://discuss.haiku-os.org/t/iceweasel-unofficial-firefox-port-on-haikudepot/16088/271

[X547]

According to user reports, issue is not present on latest Haiku Nightly version, it is only reproduced on Haiku Beta release.