MC 1.18.2
Fabric API 0.53.4
MineGate 1.2.2

To reproduce:

1. Grab a rail and a minecart
2. Place a rail down, place a minecart down and sit in it
3. Observe that you are actually hovering over the minecart
   

Affects all entities, not just the player. This is not just a visual bug either, it actually affects entities' collision box, which makes them unable to move through 2 blocks tall railways. This potentially breaks farms that have entities riding minecarts in them.

Logs: https://gist.github.com/Footage2-Amply-Pounce/b8c696813d179441bf7a1e135ef335a1

I will see to fix this problem before 1.19

After checking on my side, I don't have this problem.

Are you sure you don't have a mod that changes player size?

As much for me, I was on my dev version and unwittingly I fixed the bug by modifying things.
This will be corrected in the next version.

Fixed in the new version. (MoreBlocks 1.2.3)
Note: An improvement in the future is planned, if other similar issues exist.