When an undead mob (Zombie, Skeleton, Zombie Pigman ect.) stands on a Wither Rose they begin to take the Wither damage. When they walk off they no longer take the Wither damage.
Replicate
Place a Wither Rose
Spawn an Undead Mob (Preferably one that doesn't fly)
Thank you for your report!
We're actually already tracking this issue in MC-6091, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. That means that this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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