Mobs doesn't burn when their head/upper body in lava, while their legs in water

Hi, So there is a bug related to mobs behaviour in lava while their body/legs in water. The thing is, they now no longer burn in lava while in water. That goes same for the player. This also affect the realism (Yeah I care about realism in game and so the community), it's obvious that one must take damage/burn when in touch with lava. It doesn't make sense if the other part of its body (which is in water) preventing it from burning. It should burn! Please fix this bug.

(Sorry for bad English, it's not my language)