Frame height not shown properly in opera 10 b1

Hi guy:

I just try my site in Opera (10.00 b1) and I discovered that the forum didn't shown properly.

The "phpBB frame height" is set to 100%, but Opera shows like 90px of the forum in the frame (file attached). And Opera 10 it's 100% web standard (the acid3 stuff)

The forums shows correctly in Firefox 3.0.10, Chrome 2.0.172.28, and IE 8.0.6.

Why it's that? Any ideas?

PD: excuse my awful english, not my mother language. My first post here. I hope to contribute someway.