Description of problem:
Adding a dropdown element in a custom service dialog and selecting one of its default values shows the option "Nothing selected"

Version-Release number of selected component (if applicable):
5.11

How reproducible:
100%

Steps to Reproduce:
1. Navigate to Automation > Customization and select Service Dialogs
2. Create a new service dialog
3. Add a dropdown widget and select the edit button on the dropdown
4. Now select one of the default dropdown options, any option selected will be displayed as "Nothing Selected"

Actual results:
"Nothing Selected" from custom dropdown default option

Expected results:
Default option selected from custom dropdown

Additional info:
This bug only happens the first time when editing a dropdown menu, after the second time selecting one of the default options, the option will be properly displayed.