I had the same problem when you do a show int it says mtu 1514 but when you do a sh ip int
it will show a diffrent mtu size in mine case standard for a tunnel interface = 1476 . 1500 - gre overhead.
I don't know why its different from the sh int tunnel command . its a bit confusing. but the value with the sh ip int command changes when you change the mtu size. while on the tunnel it will still stay at 1514. So het value displayed by the sh ip int command should be considerd al the real MTU size for that interface