I tried to add to my domains an MX record but when I press the "Create" button I get an error message:

Priority Priority must be an integer between 0 and 65535

The priority value i try to add is "10".

I tried then to press the button "Add Gmail MX Records" and this works. Correctly adds the Gmail MX records. If I edit the inserted records I get the same error, even if I do not modify them and simply hit Enter.