Steps to reproduce the issue

1. Create a form field of type combo with the required attribute set to true
2. Access a screen displaying the form field
3. Select an option

Expected result

The field contains the selected option and no validation highlighting

Actual result

The field is highlighted as invalid (i.e. red, bold text and a red border) until a second valid selection is made (or another pair of focus / blur events occur on the field)

System information (as much as possible)

Joomla 3.7.4
PHP 5.6.30
Apache 2.4
Centos 7

Additional comments

• Video of issue in action: http://support-media.muckypuddle.me/lxH0
• Field XML tested:

<field name="etd" type="combo" filter="text" required="true" label="COM_XXX_FORM_LBL_XXX_ETD" description="COM_XXX_FORM_DESC_XXX_ETD" hint="COM_XXX_FORM_DESC_XXX_ETD">
      <option value="1">1 Hours</option>
      <option value="2">2 Hours</option>
      <option value="3">3 Hours</option>
      <option value="4">4 Hours</option>
      <option value="5">5 Hours</option>
      <option value="6">6 Hours</option>
      <option value="7">7 Hours</option>
      <option value="8">8 Hours</option>
      <option value="9">9 Hours</option>
      <option value="10">10 Hours</option>
      <option value="11">11 Hours</option>
      <option value="12">12 Hours</option>
</field>