WordPress MU

I'm finding the ajax for adding a custom field is busted in MU (yet works on WP 2.3.1). When you try to add a second custom field, rather than add it in addition, it seems to replace.

Anyone else seeing this? Find out the root cause?

http://trac.mu.wordpress.org/browser/trunk/README.txt

http://codex.wordpress.org/Debugging_WPMU