pfSense

When adding a new interface on the (assign) page, it defaults to the first interface that hasn't been assigned. This change is immediately applied (although the interface is not "enabled" until ticked, obviously).

If the first interface picked happens to be a CARP VIP then this VIP will stop working until the new interface is correctly assigned and the CARP interface re-saved.

Suggestion: Maybe have an "apply" button that needs to be pressed before any new interface is actually assigned, much like most of the rest of pfsense, or perhaps when you add a new interface it defaults to something that won't potentially cause issues (say, a loopback)