Do anyone know is it bug that increasing enchanting soul level and perk not able to increase the magnitude of magicka regen part of fortify skill and regen enchantment?

Are you referring to the fortify (magic skill, destruction for example) and magicka regen. The enchantment thats on the robes? I believe that one is fixed. When you raise the enchantment it only raises the skill, not the regen. Not 100% sure on this, but I think I remember that being the way it was.

It is not fixed, on 1.7 patch by the way.

I previously only use robe so don't notice much. But I was going to switch to unenchanted royal vampire armor (mod) and found out I can't increase the magicka regen magnitude. :S

It's not a bug. It's a feature. Robes are special.