With that mouse being plugged in, can you please copy&paste the output of "mtp-detect" (it's in the "mtp-tools" package, you have to install it).
Also, can you please start rhythmbox in debug mode, so that we can see what it's doing? For this, please run
rhythmbox -D mtp > /tmp/rb.log 2>&1
Wait until Rhythmbox displays and settles down, then close it again and attach /tmp/rb.log here. Thank you!
With that mouse being plugged in, can you please copy&paste the output of "mtp-detect" (it's in the "mtp-tools" package, you have to install it).
Also, can you please start rhythmbox in debug mode, so that we can see what it's doing? For this, please run
rhythmbox -D mtp > /tmp/rb.log 2>&1
Wait until Rhythmbox displays and settles down, then close it again and attach /tmp/rb.log here. Thank you!