Description of problem:
Change the disk size causes the unit changed, it's the wrong behavior as user can never get what they want

Version-Release number of selected component (if applicable):
v4.11.0 and v4.12.0

How reproducible:
100%

Steps to Reproduce:
1. add a disk and change the disk size, eg: 60 -> 6000
2.
3.

Actual results:
the unit field is changed

Expected results:
the unit field isn't changed

Additional info: