6.8 generates 30% larger files than 6.7 with same 1-pass quality based settings

I had just tested 6.7 1-pass rate control exensively when I got a poput saying 6.8 was available.
So I installed and ran a few test with the same settings as before, but now I get files that are consistently larger than before, about 30% bigger.

I'm using TMPGEnc 4.0 Xpress (4.3.1.222) with divx pro 6.7 & 6.8, tested with following settings:
- Unconstrained profile, 1-pass target quantifier 4, Encoding Better Quality, Adaptive multiple consecutive
- Home Theater Profile, 1-pass target quantifier 4, Encoding Better Quality, Adaptive single consecutive
- Home Theater Profile, 1-pass target quantifier 4, Encoding preset 5
- Home Theater Profile, 1-pass target quantifier 4, Encoding preset 5
- manual setting: -b1q 4 -pq 7600 -b 3 -windowed_fullsearch=2 -quantization=2

Does anyone has any idea why 6.8 generates bigger files than 6.7?