first a short thank for the great als slim application, nice work.
I have found, that when you close the Song History dialog not with the given button but with the normal window close button, the next time you open it, there is a slightly diferent backround color and no text.
This bug appears on my Kubuntu 12.04 system frequently. I am using the 0.7.2 Radio Tray. actually have no time to test it with other versions.
Hope, this information is helpful for you.