Error with unicode names convertation

I get this error while conversion, all names in unicode, all names are different, but script see them as identical.

Fatal conversion error
functions_phpbb20.php [ 1881 ]
Colliding usernames were found on your old board. In order to complete the conversion please delete or rename these users so that there is only one user on your old board for each clean username.

p is the clean username for:
» user id: 13 username: Р (50 posts) Ируся
» user id: 156 username: Р (6 posts) ИРИНА
» user id: 529 username: Р (0 posts) Игривая
» user id: 1084 username: Р (1553 posts) Ирина Леонидовна
» user id: 1618 username: Р (0 posts) Ирина Шумова
» user id: 3660 username: Р (71 posts) Ирина Фомичева
» user id: 4283 username: Р (0 posts) Илья
» user id: 5019 username: Р (0 posts) Ириша
» user id: 5699 username: Р (0 posts) ИванЧай
##########################

i add real username at end of every string, so you may see that script use strange name P instead of real name.