On two different computers running stock Ubuntu 15.10, I get identical behavior.
When Calibre is NOT running, plugging in my iRulu X1s tablet running Android 5.1.1 ("Lollipop") works correctly, accessing via MTP and able to see folders and files on both internal and external (SD) storage.
When Calibre 2.51.0 is running, the file manager window showing the contents of the table goes empty if it was open, and new windows open rapidly and briefly show icons for internal and external storage before going empty. A new window opens every second or so until either the device is unplugged or Calibre is shut down.
Here is the debug output produced by Calibre (device serial number redacted):
Code:
calibre 2.51 embedded-python: True is64bit: True
Linux-4.2.0-27-generic-x86_64-with-debian-jessie-sid Linux ('64bit', 'ELF')
('Linux', '4.2.0-27-generic', '#32-Ubuntu SMP Fri Jan 22 04:49:08 UTC 2016')
Python 2.7.9
Linux: ('debian', 'jessie/sid', '')
Successfully initialized third party plugins: DeDRM
USB devices on system:
[['0x13d3', '0x5188', '0x814', u'Azurewave', u'USB2.0 UVC HD Webcam',
u'NULL'],
['0x1f3a',
'0x1007',
'0x233',
u'USB Developer',
u'Android',
u'XXXXXXXXXXXXXXXXXXXX'],
['0x3eb', '0x8417', '0x1132', u'Atmel', u'Atmel maXTouch Digitizer', u'']]
No disabled plugins
Looking for devices of type: MTP_DEVICE
Unknown device USBDevice(busnum=2, devnum=16, vendor_id=0x1f3a,
product_id=0x1007, bcd=0x0233, manufacturer=USB Developer,
product=Android, serial=XXXXXXXXXXXXXXXXXXXX) claims to be an MTP device
MTP devices connected:
USBDevice(busnum=2, devnum=16, vendor_id=0x1f3a, product_id=0x1007,
bcd=0x0233, manufacturer=USB Developer, product=Android,
serial=XXXXXXXXXXXXXXXXXXXX)
Trying to open: USBDevice(busnum=2, devnum=16, vendor_id=0x1f3a,
product_id=0x1007, bcd=0x0233, manufacturer=USB Developer,
product=Android, serial=XXXXXXXXXXXXXXXXXXXX)
Opening device failed:
Traceback (most recent call last):
File "site-packages/calibre/devices/mtp/unix/driver.py", line 147, in
debug_managed_device_detection
File "site-packages/calibre/devices/mtp/driver.py", line 124, in open
File "site-packages/calibre/devices/mtp/base.py", line 24, in synchronizer
File "site-packages/calibre/devices/mtp/unix/driver.py", line 216, in open
OpenFailed: Failed to open USBDevice(busnum=2, devnum=16,
vendor_id=0x1f3a, product_id=0x1007, bcd=0x0233, manufacturer=USB
Developer, product=Android, serial=XXXXXXXXXXXXXXXXXXXX): Error: Unable
to open MTP device with busnum=2 and devnum=16, tried 1 such devices
Looking for devices of type: SMART_DEVICE_APP
All IP addresses {'lo': [{'peer': '127.0.0.1', 'netmask': '255.0.0.0',
'addr': '127.0.0.1'}], 'wlan0': [{'netmask': '255.255.255.0', 'addr':
'10.0.0.46', 'broadcast': '10.0.0.255'}]}
No device is connected
Looking for devices...
Devices possibly connected: None