As discussed on the ML : https://groups.google.com/d/topic/liftweb/rjySEZqZiik/discussion

Currently MongoMapField.toForm is defined as follows:

def toForm = Empty //FIXME

So it's impossible to override it with anything other than a method returning Empty.

(this problem affects MongoCaseClassField, MongoCaseClassListField and PatternField)
It used to affect MongoListField, but it has been fixed.

I've written a fix for this : ( https://github.com/divarvel/framework/commit/2356199bfea3db26f3854d83e7c55d3c63b2436c,https://github.com/divarvel/framework/commit/ba4a0e9b47f1758ad32e78af7ecb034138f928a7 and https://github.com/divarvel/framework/commit/5ed34281fcc0074a06b9f1f6803252be6faff844 ).
I hope it can help