Description of problem:
This bug has been introduced when fixing bug 1328498. LUC reports that the "drive is in use" every time some partition is mounted, even if the partition gets unmounted fine. So right now, if you insert a flash drive and is automounted, the first time you click "Write to disk" you'll receive "drive is in use", and the second time you click on it, it starts writing. 100% reproducible.

So either there is a code sequence error:

  if mounted:
    print error
  unmount

instead of

  unmount
  if mounted:
    print error

or there is some race condition between unmounting finishing and LUC refreshing the mounted status.

Version-Release number of selected component (if applicable):
liveusb-creator-3.93.2-1.fc24.noarch

How reproducible:
100%

Steps to Reproduce:
1. insert a flash drive and mount some partition
2. make sure the partition is not being used, i.e. can be unmounted
3. in LUC click Write to disk
4. see error "Drive is in use" in LUC
5. see that the partitions were unmounted OK
6. click Write to disk again, see that writing starts