clearing MTU field on interface doesn't set back to default
If you set an interface's MTU on interfaces.php, save and apply changes, then clear the MTU field so there is nothing in it and save and apply changes again, the MTU doesn't change back to the interface's default as the text says it will use until you reboot.
For instance, set an Ethernet interface to 9000, save and apply and you'll see 9000 in ifconfig. Blank out the MTU field, save and apply changes, and it should switch back to 1500. You'll see it stays at 9000.
Work around: set 1500 there instead of just clearing the field, and it'll be correctly updated.
Not a regression, not targeting 2.2.