Comment 2 for bug 725097

Sorry, I see now that the description is unclear. It happens when you use an ISO file as a drive letter.

For example:
1) Start with two standard drive letters: C as ../drive_c and Z as /
2) Add D letter and set device field to iso file
3) Add E letter and set it to another iso file
4) When you select D, the device field updates to correct path.
5) When you switch to E the device field updates as expected.
6) When you switch to C or Z the device field remains unchanged.

And if you check the " "use device file for path" checkbox after selecting an iso file in device field, it remains visible when you switch to other drives - and the path field also stays "grayed out".