Curious that all the skins have the same problem.
It seems to be due to a problem with back.bmp (in the skins folder). It's not logical, because the background is taken in the skin folder, and not common to all the skins.
Is the background checked or unchecked (F2 > Gui appearance > Skin > Display toolbar background) ?
Have you try to set and unset it (or the contrary) with a K-Meleon restart between each change, to see if it's better ?
A+
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Web:
http://jujuland.pagesperso-orange.fr/
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc