I don't know if this is intended, but they don't usually stack with other versions of the buff, and they even overwrite higher versions (for example, the 2hp regen potion overwrote my chloroplast spell).
The only potion i've seen stacking is the 1mana regen, which stacks with clarity 2 (did to me) but doesn't stack with invis (bug for sure).
The only potion i've seen stacking is the 1mana regen, which stacks with clarity 2 (did to me) but doesn't stack with invis (bug for sure).