Yes it's still an issue with 1.13-pre6. However I believe this can be closed as a duplicate of MC-130857
I found out that the issue was caused by a plugin and not by Minecraft itself
Can confirm this!
Yes this issue is still in the latest versions.
It seems like this is a client side issue.
Since event with sending the update packet (132TileEntityUpdate) the mob doesn't change.
(Client doesn't handle the packet right?)
See here e.g. the bukkit ticket -> https://bukkit.atlassian.net/browse/BUKKIT-2630
Yes this still an issue with 1.13-pre6