As usual while waiting for the next release - don't forget to check the nightly builds in the forum.
you can try Settings->Environment->Notebook appearance->Tabs style
Is there any chance that your wxGTK is built against GTK3?In GTK3 the native tab art is not available, and after a fast search I wasn't able to find an easy way to reimplement it, so we'll need to do something to prevent this ugliness...