Bug when create reference field in type after upgrade to version with default value

Hello,
i found bug in application with reference field in type.
When i created new reference field in type ( after upgrade to version with default value) like


and i leave empty Field Deafult Value and save this

Next
I go to list of objects in this type nad i clicked add new object and i see that:

Why this field is fill if i don’t set and Default Value?

Curiosity
When i have reference fields which are created before version with default value these fields work good