Certain potion effects are applied incorrectly when repeated

The bug

Certain potion effects are applied incorrectly when repeated (e.g. when throwing potions too fast or using a repeating command block).

Examples

(Use a repeating command block to execute this command repeatedly.)
Applying /effect give @p minecraft:poison 34 repeatedly results in no damage taken regardless of the player's current health.
Applying /effect give @p minecraft:poison 30 repeatedly results in taking damage up to twice a second, instead of once every 1.25 seconds.
Applying /effect give @p minecraft:regeneration 30 repeatedly results in healing every time the effect is applied, instead of once every 2.5 seconds.
Applying /effect give @p minecraft:regeneration 31 repeatedly results in no healing actually being applied.

Original description

If I throw a custom potion with poison on myself rapidly (getting the potion in one inventory slot through a command block) I wont get damage until I stop throwing them.

Command for potion:

/replaceitem entity @a[score_kit_min=9,score_kit=9] slot.hotbar.1 minecraft:splash_potion 1 0 {display:{Name:"Some potion with poison",Lore:[CAUTION! LETHAL!]},CustomPotionEffects:[{Id:19,Amplifier:2,Duration:60}],Potion:"minecraft:awkward"}

I tried to upload a video, but it didn't work (even under 10MB File size there was an internal server error but the strange thing is, I can't upload it to youtube either, idk.)