numeric usernames in 7.3.1?

We use fully numeric usernames in 7.2.1 (e.g. '1001').

When generating 7.3.1 from 7.2.1's dump, everything seemed to be OK, but we
can't login with such usernames.

Is it a new behaviour in 7.3.x? Is there a configurable option or an easy
way to modify the source to retain the old behaviour? Or is the only way to
rename all the users?

Yours,
G.
--
while (!asleep()) sheep++;

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