When using the /effect command, the potion effect is given at the level requested +1. Speed 2 gives speed three, regeneration 1 gives regeneration 2, etc. Created new worlds, and rebooted the game. Also, tested with a friend and it seemed to actually double the effect instead of it just being a visual glitch. (Very crude tests)
this is WAI (MC-10462 and MCPE-65135)
if you need (Effect) I, use /effect @p (effect) (time) 0