Fall damage bug?

[CyberWolf]

Started playing tekkit lite 0.5.9 today, after a while I noticed something strange: Somehow I was hardly taking any fall damage I would jump from 6 or so blocks high and would take no damage at all. Seemed a bit strange because jumping down 4 blocks would hurt in vanilla, this seems to be happening randomly sometimes I take damage while other times I don't. Now I'm not sure if this is a bug or intended due to some mod that is in lite. Could someone shed some lite on this? (see what I did there?)

Also, I installed Optifine onto it, could that be a reason?

[Teraku]

What kind of armor do you have on you when this happens? And which items are present in your inventory?

You know what, the next time this happens, just screenshot your entire inventory, it might be a certain item.

[CyberWolf]

This started happening fairly early on, no armor on and my inventory was fairly empty (literally 15 mins into the world)

I even made a new world just to check this out. Entered the world, built a tower of 6 blocks again, jumped down, nothing happened. Once again no armor and nothing in my inventory.

Edit: okay I just tried jumping from the cloud layer, roughly 40-50 from the ground

Did not lose a single heart. This is so random.