I think the reason of this bug is same as bug#12508. From revision#67849, we start to draw the tool bar buttons ourselves, not using the native tool bar widgets anymore. I have tested this problem on my Solaris 10 32bits which installed on WMware, but it doesn't have the problem (you can see it in attached snapshot). Maybe it's a GTK version related problem. I'm finding a lower GTK version Solaris now.