Why XviD doesn't follow the B-VOPs ratio/offset settings on 1-Pass Q-based encodes?

[jsquare]

Most of my encodes are 1-Pass fixed Q or Bitrate based, and can't get a XviD to comply with the B-VOPs settings on Q based encodes. For example if I want to encode at Q=2.5 with default B-VOPs settings 2-1.5-1, or even when I change the B-VOPs settings to 2-1-2 I'll get (P2-B4-B4-P3-B4-B5...) See the display encoding status:9939

When I should be getting (P2-B4-B4-P3-B5-B5...), but it works fine with Bitrate encodes.
Is this normal or is there a bug on XviD?

[Brother John]

Consecutive B frames should always have the same (frame) quantizer because of the way the B quant formula works. How did you analyse that P2-B4-B4-P3-B4-B5 sequence? It’s not apparent from the screenshot.

[jsquare]

Consecutive B frames should always have the same (frame) quantizer because of the way the B quant formula works. How did you analyse that P2-B4-B4-P3-B4-B5 sequence? It’s not apparent from the screenshot.
Just updated the screenshot with the sequence in question showing on Xvid Status log window.

[henryho_hk]

Are the two consecutive B-frames' quant based on the previous I/P frame or the specified CQ in this mode? It looks like the latter.

CQ = 2.5 .... so average B-frame Q should be 4.75.... and we are getting 4 followed by 5...

[Brother John]

Afaik know they’re based on the two surrounding I/P quants. Probably someone who knows the Xvid code can clear this up best.