Description of problem:

I added a disk to a vm with teh same alias as an existing name and first my UI crashed and than my computer (with cpu overload). 
this only happens when you try to create the disk from the Disks sub tab in the vm's main Tab. 

Version-Release number of selected component (if applicable):

si4

How reproducible:

100%

Steps to Reproduce:
1. create a vm with disk
2. create a second disk and give it the same alias as the existing disk
3.
  
Actual results:

firefox will crash (stop script message will appear), after 2 minutes my laptop crashed 

Expected results:

we should be able to create the disk

Additional info: