I use Mandriva KDE - have never used Gnome! Rather than describe what goes wrong, I'd rather just say that behaviour under Windows is perfect.
Question: do comboboxes in other KDE applications under Mandriva behave different than the comboboxes in Lazarus?
If so, it possibly is a bug in the widgetset, so in that case please describe how they behave differently.
...with the seeming virtual cessation of Lazarus development ...
Did you actually look at the link theo provided?
Remeber, no one of the developers of Lazarus or FreePascal gets paid for this, we are all volunteers.
You seem to be unwilling or unable to help the development of Lazarus yourself by contributing code/patches to the project.
That's OK though, but only complaining that we (the community) did not fix something that we feel is not a bug, isn't very helpfull either.
Bart