The tabbed dialogs in recent build do not eraase background when switching tabs.
This is regression introduced since November 20.
Timofeev, was it you?
Yes, I am to blame, indeed... Thanks for the report.
Ivan Timofeev committed a patch related to this issue.
It has been pushed to "master":
fdo#57472: VclContainer: make it paint-transparent
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.
*** Bug 57499 has been marked as a duplicate of this bug. ***