Steps to reproduce:

1. Click button "Populate"
2. Open ComboBox
3. Close ComboBox
4. Open it again - popup width changes
5. Select any value - button width changes

Restart app
1. Click "Set editable"
2. Click "Populate"
3. Open ComboBox
4. Close ComboBox
5. Open ComboBox - popup width changes
6. When value is selected button width remains the same