Just quick info for the moment.

When I enter a TCW 0.70 world directly in the Underdark Layer in single player with cc904/cwg29 Forge 2658 I cannot throw enderpearls.

If I TP to the surface I can throw them again, then if I TP back to the Underdark I can then throw and use the enderpearls.

I then waited for a couple minutes and could still throw them. I then logged out from in the UD and back in and again could not throw them until I had TP'd to the surface. This was all in Creative mode.

I will troubleshoot more at another time when I have time.