Steps to reproduce:

1. Created a new host.
2. Add one interface as primary.
3. Make sure everything is valid for the host except the mac.
4. Try to save.

Expected:
Validation error about the invalid mac.

Actual:
The error in the attached screenshot.

This only happened for an interface that I marked as Managed, Provision.
If I check disable build mode and mark the interface just primary with nothing else I get a expected validation error.