You can see if this helps out at all:

http://lists.horde.org/archives/cvs/Week-of-Mon-20070101/064445.html



But looking at the code, we have always checked to see if the folder 
name we are trying to rename is empty or not.  So you may have to 
manually check your identity entries for bad data if this fix doesn't 
work - since I can't reproduce this at all.

At the start of the month, I get the following action:



The current folder(s) "sent-mail, " will be renamed to 
"sent-mail-dec-2006, -dec-2006".



There seems to be an extra ",-dec-2006" appended. also, the action 
does not happen.