On my wireless network, I can tracepath to a mac using MTU of 1500 on Ubuntu linux 12.04.
(Mac MTU is set to 1470 for some reason, but reply frames are not that big so this does not matter)
When I tracepath to my HP printer, it never responds to any frame that is 1514 bytes long: MTU(1500) + Ethernet(14) (SRC(6) + DST(6) + type(2)) = 1514
But if I set my MTU to 1498, my printer responds. An MTU of 1499 fails also.
Note: Setting MTU to 1500 on my Mac causes printing to fail as well so I doubt it is anything to do with either computer, nor my router.
Update: If I tracepath to google.com I can see my router (on its WAN link) reply with ICMP packets stating that fragmentation is needed and subsequent frame MTU needs to be 1474.
tracepath changes frame size to match this and continues. This means it now sends frames that are 1488 bytes long.
For my printer, it does not send back any ICMP packet stating that it can not process a 1500 byte payload. It is as if it is black-holing frames larger that 1512 bytes.