Hopper minecarts under water will not function under water while clipped into a block.

Steps to reproduce:
1. Clip a hopper minecart into a block using a piston
2. wait for the cart to sink into the block so the top is not visible
3. set it up as water trench with the minecart being at the end as in the screenshots
4. add water to the trench and drop blocks in.
5. The blocks will pass over the minecart and then teleport to the blog immediately after it.

Notes:
-Transparent blocks do not fix the issue.
-The effect is present with both still and moving water blocks
picking the water up with a bucket does not fix the problem, the items must be manually picked up, the water removed and then the items redropped
-Normal hoppers do not have this problem