While sneaking, a fishing rod cannot be cast using the Right click Button while facing usable blocks. It is, however, possible to cast it while sneaking and not facing usable blocks. 

Steps to reproduce:

1. Take a fishing rod. 
2. Enable new touch controls and start sneaking. 
3. Face a non-usable block like grass and cast the fishing rod using a right click.
4. Record the result.
5. Face a usable block like crafting table or chest and cast the fishing rod using a right click.

Expected results:

The fishing rod is cast in both the cases while sneaking.

Observed results: 

The fishing rod is cast only while facing a non-usable block, while it does nothing while facing a usable one. 

In the below video, a water bucket can be used to waterlog or place water in front of a usable block while sneaking, while it isn't possible to cast the fishing rod in same conditions.