I did an in depth review of that case and it appears that the way we calculate the number of pyramid level was not the same as the one done before by smartblend. This old algorithm is doing less levels than we did ( or saying other way, we are doing too much levels compared to the old algorithm ). When looking at the results carefully, it seems that we do too much. See the following screenshots : it's level 0 ( meaning the maximum number of levels ), level -4 ( meaning all except 4 last levels ) and -2 ( meaning all except 2 last levels ).
It appears that the right settings is -4 ( which could be compared to the real 0 of smartblend ). So we have 2 solutions : either we change the way we calculate the level max level to correspond to smartblend, or we change the default setting to -4 for multiband in the new engine.
Both solution are okay in fact. So for Thierry, just switch to -4 and it will be okay with beta 2.