Xvid bitrate and file size problem - Heeelp!

[Salinas]

Hi Everybody!

I have a very distressing problem with an x264 mkv! This is an episode of a series, and I want to encode it to an Xvid format with 2 passes! With another episodes I made it four times before. And everything went fine... I calculate the bitrate, and encode it to the correct size.
But now I get a size with 40 MB smaller, and I put the bitrate vainly higher up, I get a size of the same size for a byte.
The calculated bitrate is 1050, I tried it with 1200 and 1400, and everytime I get the same size! :S
I use meGUI, and I tried with easyXvid encoder too with simiar outcomes.
When I look the properties in MPCHC, it writes 907 for bitrate, and with bitrate calculator this is roughly equals to the output size...
I have no idea, what is the problem...
There are the Xvid config dialogs:
http://members.upclive.hu/bandt.kft/scshot1.jpg
http://members.upclive.hu/bandt.kft/scshot2.jpg

Please, help me!
THX in advance!