The mounting bosses on the 400 ones are slightly shorter, fitted some on mates ZS. Easily sorted by supergluing some washers to the bosses. Theres probably less than 1mm difference but its enough to distort the handles when tightened up.
Broken handles can be fixed, see the pdf towards end of this thread.
http://forums.xpowerforums.com/showthread.php?t=29077