I get the same error when clicking the eject-symbol on a mounted Android phone (Galaxy S3 Mini). As mentioned earlier, using right-click -> unmount works without errors.

I'm using Ubuntu 13.10, GNOME Shell 3.8.4 and GNOME nautilus 3.8.2.

These are the corresponding syslog lines:

(Plugging Android device in)

Dec 29 15:23:04 schwarzekiste kernel: [   39.619726] usb 1-4: new high-speed USB device number 4 using ehci-pci
Dec 29 15:23:04 schwarzekiste kernel: [   39.753127] usb 1-4: New USB device found, idVendor=04e8, idProduct=6860
Dec 29 15:23:04 schwarzekiste kernel: [   39.753132] usb 1-4: New USB device strings: Mfr=2, Product=3, SerialNumber=4
Dec 29 15:23:04 schwarzekiste kernel: [   39.753134] usb 1-4: Product: Android
Dec 29 15:23:04 schwarzekiste kernel: [   39.753135] usb 1-4: Manufacturer: Samsung
Dec 29 15:23:04 schwarzekiste kernel: [   39.753137] usb 1-4: SerialNumber: XXXXXXXXXXXXXXXXX
Dec 29 15:23:04 schwarzekiste colord: Device added: sysfs-Samsung-Android
Dec 29 15:23:09 schwarzekiste dbus[488]: [system] Activating service name='org.freedesktop.hostname1' (using servicehelper)
Dec 29 15:23:09 schwarzekiste dbus[488]: [system] Successfully activated service 'org.freedesktop.hostname1'
Dec 29 15:23:17 schwarzekiste whoopsie[996]: online
Dec 29 15:23:39 schwarzekiste kernel: [   74.482857] perf samples too long (2505 > 2500), lowering kernel.perf_event_max_sample_rate to 50000

(Clicking eject)

Dec 29 15:23:42 schwarzekiste kernel: [   77.978892] ------------[ cut here ]------------
Dec 29 15:23:42 schwarzekiste kernel: [   77.978904] WARNING: CPU: 2 PID: 2646 at /build/buildd/linux-3.11.0/drivers/usb/host/ehci-hcd.c:1038 ehci_endpoint_reset+0x101/0x110()
Dec 29 15:23:42 schwarzekiste kernel: [   77.978905] clear_halt for a busy endpoint
Dec 29 15:23:42 schwarzekiste kernel: [   77.978907] Modules linked in: pci_stub vboxpci(OF) vboxnetadp(OF) vboxnetflt(OF) vboxdrv(OF) snd_hda_codec_hdmi intel_powerclamp kvm_intel(F) kvm(F) gpio_ich parport_pc(F) ppdev(F) rfcomm bnep bluetooth snd_hda_codec_realtek microcode(F) snd_hda_intel snd_hda_codec serio_raw(F) snd_hwdep(F) snd_pcm(F) snd_seq_midi(F) snd_seq_midi_event(F) snd_rawmidi(F) snd_page_alloc(F) snd_seq(F) lpc_ich snd_seq_device(F) snd_timer(F) snd(F) nvidia(POF) soundcore(F) drm coretemp mac_hid mei_me mei lp(F) parport(F) pata_acpi hid_generic usbhid hid usb_storage(F) firewire_ohci firewire_core crc_itu_t(F) r8169 mii(F) pata_jmicron ahci(F) libahci(F)
Dec 29 15:23:42 schwarzekiste kernel: [   77.978944] CPU: 2 PID: 2646 Comm: pool Tainted: PF          O 3.11.0-14-generic #21-Ubuntu
Dec 29 15:23:42 schwarzekiste kernel: [   77.978946] Hardware name: Gigabyte Technology Co., Ltd. H55M-USB3/H55M-USB3, BIOS F11 11/01/2010
Dec 29 15:23:42 schwarzekiste kernel: [   77.978947]  0000000000000009 ffff8801d6559d08 ffffffff816e593a ffff8801d6559d50
Dec 29 15:23:42 schwarzekiste kernel: [   77.978951]  ffff8801d6559d40 ffffffff81061dbd 0000000000000003 0000000000000086
Dec 29 15:23:42 schwarzekiste kernel: [   77.978953]  ffff880210410800 ffff880210410a84 0000000000000246 ffff8801d6559da0
Dec 29 15:23:42 schwarzekiste kernel: [   77.978956] Call Trace:
Dec 29 15:23:42 schwarzekiste kernel: [   77.978962]  [<ffffffff816e593a>] dump_stack+0x45/0x56
Dec 29 15:23:42 schwarzekiste kernel: [   77.978966]  [<ffffffff81061dbd>] warn_slowpath_common+0x7d/0xa0
Dec 29 15:23:42 schwarzekiste kernel: [   77.978968]  [<ffffffff81061e2c>] warn_slowpath_fmt+0x4c/0x50
Dec 29 15:23:42 schwarzekiste kernel: [   77.978973]  [<ffffffff8104dee9>] ? default_spin_lock_flags+0x9/0x10
Dec 29 15:23:42 schwarzekiste kernel: [   77.978975]  [<ffffffff81534571>] ehci_endpoint_reset+0x101/0x110
Dec 29 15:23:42 schwarzekiste kernel: [   77.978979]  [<ffffffff8151eaa5>] usb_hcd_reset_endpoint+0x25/0x70
Dec 29 15:23:42 schwarzekiste kernel: [   77.978982]  [<ffffffff81520a78>] usb_reset_endpoint+0x28/0x40
Dec 29 15:23:42 schwarzekiste kernel: [   77.978984]  [<ffffffff81520afe>] usb_clear_halt+0x6e/0x80
Dec 29 15:23:42 schwarzekiste kernel: [   77.978987]  [<ffffffff8152bc9f>] usbdev_do_ioctl+0xa8f/0xf30
Dec 29 15:23:42 schwarzekiste kernel: [   77.978989]  [<ffffffff8152c16e>] usbdev_ioctl+0xe/0x20
Dec 29 15:23:42 schwarzekiste kernel: [   77.978993]  [<ffffffff811b8c55>] do_vfs_ioctl+0x2e5/0x4d0
Dec 29 15:23:42 schwarzekiste kernel: [   77.978996]  [<ffffffff811b8ec1>] SyS_ioctl+0x81/0xa0
Dec 29 15:23:42 schwarzekiste kernel: [   77.978999]  [<ffffffff816f571d>] system_call_fastpath+0x1a/0x1f
Dec 29 15:23:42 schwarzekiste kernel: [   77.979001] ---[ end trace f5b367630068bcfe ]---
Dec 29 15:23:42 schwarzekiste kernel: [   77.981079] usb 1-4: usbfs: process 2508 (events) did not claim interface 0 before use