Unicode issues when groups have non ASCII chars in name

[keul]

I found an issue (probably the same at plone/plone.app.ldap#3) but fully reproducible using basic Plone groups. Plone 4.3.4.

the @@new-user page display at bottom a list of groups, to directly add users inside.

A group id like AcQuaRI_nonconformità ("'AcQuaRI_nonconformit\xc3\xa0'") give the issue and unluckily Plone allow this kind of ids for groups.

I found a way to fix the UnicodeDecodeError changing two products, plone.app.users and plone.app.form. See 8585f0c and plone/plone.app.form@399dc85

Still the issue is not fixed: the @@new-user view is now loaded and works, but selecting the group with the bad id will raise a validation errore (invalid value).

Any tips?