Steps to reproduce:

• Create / edit a host
• Go to the network tab
• Add an additional interface
• Fill all fields but the mac address
• Save

Expected results:

An error that mac address is required.

Actual results:

It saves the host, but drops the extra interface.

On a related note, changing host puppet parameters has a similar bug that it can ignore invalid input and just drop all your changes I heard from a colleague, but haven't looked into it.