The command works perfectly fine if it's any faction but 'slave'. Hmm. Can anyone who's taken control of the eleutheroi at some point using 'control slave' leave a message so I can at least know for sure it's possible?

... Sigh. Maybe I'll reinstall EB, see if that helps. Or see if I can switch to eleutheroi in a game that's not about to ctd on their turn, perhaps.