Created attachment 1331010 [details]
screen-shot reference for reported issue

Description of problem:
While cancelling 'Create New Host aggregate' page with empty values, warning message popped up "Please select an item in the list"

Version-Release number of selected component (if applicable):
5.8.2.1.20170925150507_8770490 

How reproducible:
Always

Steps to Reproduce:
1. In cfme, navigate to Compute - Clouds - Host Aggregates
2. Click Configure - Add a New Host Aggregate
3. Click Cancel button with out selecting/providing any values
4. Warning message shown "Please select an item in the list"

Actual results:
Warning message related to required values shown while cancelling the action, seems the timing of message is inappropriate!

Expected results:
Instead of warning message a tool-tip on mouse hover would be helpful.

Additional info:
Screen-shot attached.