Tenser's Transformation attack bonus fades too soon

[Aradin]

Description
==========
When casting Tenser's Transformation, the following benefit "+1 attack bonus for every 2 caster levels" sometimes ends too early, leaving you swinging and whiffing until the spell duration runs out and/or the polymorph ends.

Steps to reproduce
----------------------------
Cast Tenser's Transformation, wait.

Expected result
-----------------------
The attack bonus the spell provides lasts the entire duration of the spell (1 round/caster level).

Actual result
-------------------
The attack bonus the spell provides ends unusually soon. All other effects of the spell last for the full duration. Over extended gameplay usage, it doesn't seem to happen every single time, and there's no rhyme or reason for when it does happen.

Notes
---------
This bug is particularly noticeable when using metamagic to extend Tenser's Transformation. I don't think this is a problem with extended spell, rather that the extended duration just highlights how soon the attack bonus fades.
I'm a level 23 sorc / 3 blackguard, if that makes a difference.

[Aradin]

Update! I found the source of the AB bonus disappearing: area transitions. Whenever you transition through an area while polymorphed, the AB disappears.