Hi Toure Yaya, Inte frames (P and B) are allowed to use Intra MBs. This is useful for example if new objects appears or if it is a scene change, then having Intra MBs would make more sense.
No sure which H.264 encoder are you using, however as an example our H.264 HP encoder for C66x permits you to modify this behaviour in its configuration params accordingly with the picture type
>>>from encoder.cfg>>>>>>
enableIntraPartition = 4 # 0 => INTRA_PARTITION_NONE , 1 => INTRA_PARTITION_ISLICES, 2 => INTRA_PARTITION_IPSLICES, 3 => INTRA_PARTITION_IBSLICES, 4 => INTRA_PARTITION_IPBSLICES.
thank you,
Paula