Certain theme name/folder gives the string "Array" instead of showing blocks

I have a theme with a certain name, "mytheme", placed in themes/mytheme, and for some reason it now displays only the string "Array" instead of blocks. I can turn on or off blocks and move them around, I just get different placings of these strings (eg. lots of "ArrayArrayArray" in my sidebars). If I "cp -a themes/mytheme themes/mytheme2" I get a working theme called "mytheme2" - no problem with this one, while removing all files from themes/mytheme and putting eg. bluemarine/*.* into that folder still gives me the string "Array" instead of showing my blocks.

So some database setting connected to that folder name is making the blocks for that theme name not print - anyone got an idea how to fix this?