[Setup] plone 2.5 : problem with user name with a -

[pouns]

Hi,
I'm trying to migrate some plone 2.2 to 2.5. In one of these, i have
users with username like xxx-xxxx (i know, it's not good, i'm trying to
change this). In plone 2.5, when one of these users first login, plone
create a new directory with an url like xxxx--xxxxx and my user can't
find his documents...
So, is there a way to change this ?
Thanks