Comment 66 for bug 1021375

Same for me, on Ubuntu 14.04. Try those steps.
1. get a pen drive having a read-only switch.
2. plug in pen drive in write mode
3. check you can write something.
4. Reboot
5. plug in pendrive having read-only switch on
6. check you cannot write
7. uplug normally, do not reboot pc
8. change pendrive switch position to writable
9. plug in pendrive
10. you should see from terminal write permission is OK (and you can make copies by using terminal) but "paste" is disabled in nautilus, and every writing is impossible (you cant paste or create new files).