its buggy because as of mybb 1.2x ( i could be wrong in what version) you have to edit the postbit_author_user to display the kind of thing shown in that screenshot....
Quote:[Ready!]vBulletin Orjinal Postbit Menu
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Info:
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Mod Name: vBulletin Postbit Menu
Coder: MiRaBiLiS ([email protected])
Version: 1.2
Support: MyBB 1.x <--see here
File Password: MiRaBiLiS
and as for the postbit...open admincp>templates>"YOUR THEME">modify/delete>posbit templates>postbit_author_user>
then add fieldset and legend as required...should solve ur problem