Thanks for looking into it. I managed to go back to the default theme by restoring my back-up and manually copying .emoticoncache. The reset to default theme script, like the script to change the original theme, gives me a lot of permissions errors and both just gives me red blocks in place of icons.

I wonder if this problem occurs only on specific handsets/FW versions?

Mine is PR1.1 (20.2011.40-4_PR_005)