Eu também tive o problema que meu "asus padfone infinity" não foi montado através do mtp. (adb trabalhou embora).
A solução foi conectá-lo através de uma das portas USB3 do meu thinkpad em vez de uma porta usb2. Parece que a porta USB2 não é reconhecida como usb2, ou são devicenames para usb2 "usb1"?
syslog ao conectar-se à porta USB2 :
Feb 21 13:59:55 t530 kernel: [39597.968522] usb-storage 1-1.2:1.2: USB Mass Storage device detected
Feb 21 13:59:55 t530 kernel: [39597.968634] scsi16 : usb-storage 1-1.2:1.2
Feb 21 13:59:55 t530 mtp-probe: checking bus 1, device 7: "/sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2"
Feb 21 13:59:55 t530 mtp-probe: bus: 1, device: 7 was not an MTP device
Feb 21 13:59:56 t530 kernel: [39598.966743] scsi 16:0:0:0: CD-ROM ASUS Device CD-ROM 0000 PQ: 0 ANSI: 2
Feb 21 13:59:56 t530 kernel: [39598.971140] sr1: scsi-1 drive
Feb 21 13:59:56 t530 kernel: [39598.971427] sr 16:0:0:0: Attached scsi CD-ROM sr1
Feb 21 13:59:56 t530 kernel: [39598.971580] sr 16:0:0:0: Attached scsi generic sg3 type 5
Feb 21 14:01:02 t530 kernel: [39665.530135] usb 1-1.2: USB disconnect, device number 7
Conectando à porta usb 3.0 :
Feb 21 14:01:06 t530 kernel: [39669.292066] usb-storage 3-1:1.2: USB Mass Storage device detected
Feb 21 14:01:06 t530 kernel: [39669.292231] scsi17 : usb-storage 3-1:1.2
Feb 21 14:01:06 t530 mtp-probe: checking bus 3, device 2: "/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1"
Feb 21 14:01:06 t530 mtp-probe: bus: 3, device: 2 was an MTP device