v8.1.5 and earlier
Similar to UDT Definition system.tag.configure Regression
Removing a UDT definition that has instances and then re-adding the UDT definition back in will cause all instances to have any property overrides (apart from UDT parameters thank the FSM) to be wiped. Scary stuff!!
This is particularly worrisome as someone could accidentally delete the wrong UDT definition, realise, copy it back in (because they had the nous to back it up) only to then realise that all overridden properties for UDT instances of that type are now completely gone with no way to get them back…