When placing a water bucket onto a wall you can fill the bucket again with the same source while leaving the water source block in place.

Expected behavior:
Water source block should disappear after filling the bucket with it

How to reproduce:
1. Place water bucket on a vertical surface
2. Immediately after water starts to flow to adjacent blocks right click with bucket to fill again.

Might take a few tries to get right. This issue does not take place outside of Realms.