strange problem regarding author permalink in wordpress 2.8.4

I run a multi author blog in which one of the authors has got the user_id: adnanul.haque .

after upgrading from wordpress 2.7 to 2.8.4 I found a pretty strange matter.

all the posts written by user: adnanul.haque is shown under the permalink: https://www.example.com/author/adnanulhaque but previously before upgrading it was: https://www.example.com/author/adnanul.haque/

i checked and re-checked my user list. there is no user having the id : adnanulhaque but adnanul.haque.

then how come the . (dot) is avoided in permalink? is it a bug or something is going wrong with my site?