When launched by TNT at a high velocity, you may randomly stop for no good reason. No error messages are given in chat or else where.
This is inside a funnel the same dimentions as the launcher (3x3x

I expected to be launched to around 500~ blocks on the Y axis as I have before.

When using the same launcher, I will stop at a random point whilst flying up. I then start to fall.

Although it seems to be inconsistent, it can be reproduced.

Steps to Reproduce:
1. Create a TNT launcher using dispensers in a 3x3 region, two blocks deep with all dispensers activating at the same time. (as seen in the attachment)
2. Add a tall funnel upwards in the same 3x3 region roughly 8 blocks above the launcher. (see the next attachment)
3. Stand on the fence post and activate the launcher.
Either you will
-Fly up to 500~ blocks high
-Suddenly stop at a random point whilst flying up as if you hit a block. (Between 100 and 300 blocks)

4. Repeat step two if you flew up like normal.