I used version 883, so I did not verify this with the latest version:

Whenever a player dies while standing in a liquid, like a river etc, the grave won't appear so that all inventory items would get lost.

Other mods place the graves on the next free block next to the liquid. It would also be OK to simply put the grave where the player died, floating in the water, instead of losing the inventory completely.

Again, we no longer support the grave blocks, as they are pending deletion.