Better Portals version: 0.1.3

Tested with a thrown item entity (an ItemPhysic item entity to be precise). When throwing an item through a portal that would then have the velocity to pass through a secondary portal, it would be expected for it to return to your current world, but instead, it passes through the second portal without teleporting and remains in the other world.

On further thought, this may be related to entity portal cooldowns. If it is cooldown related, I think the cooldown should be worked around, as it feels quite counter-intuitive when the portal in this mod is rewritten to be effectively instant for players.

I am unable to reproduce this. The item returns back through the other portal for me every time. I tried portals right next to each other and with one block distance between and lying ones with considerable vertical distance.
BP uses almost none of the vanilla portal code, so cooldowns shouldn't be an issue.

Oh, I only just now realized that by (an ItemPhysic item entity to be precise) you meant the ItemPhysic mod.