The bug
Frost walker ice, created by using the Frost walker enchantment on water; only has an collision box for entities.
This creates the following bugs (may be incomplete):
You can't use splash potions on the frost walker ice, they fall straight through it *.
* Eggs, snowballs, arrows (any projectile) will also fall straight through the ice.
You can mine through the frost walker ice.
You cannot place blocks on the ice.
Thank you for your report!
We're actually already tracking this issue at MCPE-41256, so we will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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