Not a coding bug, but a serious issue that I think deserves reporting here.
Change log says:
[2009-05-12] NEW: multiple-valued fields can now also be created via 'Format value' actions (values separated by \\).
This breaks action script compatibility.
E.g. whereas previously
Format value ARTIST := aaa\\bbb
Format value COMMENT := %artist%
set Comment to aaa\\bbb, now it is aaa.
Worse, there's no way of escaping this. E.g 'aaa\\bbb' makes no difference.