Icon selection in BasicButtonUI was cleaned up by the fix to 5049549. An inspection of the code for SynthButtonUI for the purposes of cleaning it up revealed a very confusing code path, and likely incorrect use of icons. For example, why does Synth use the selected icon for the pressed state and the rollover state if pressed or rollover icons don't exist. I hoped to clean this up together with 5049549 but it is riskier as we need to figure out what the code is trying to acheive, make it correct, and ensure we don't break GTK in the process. Hence this new bug.