On Special:Renameuser, the form fields don't have an id attribute. Therefore, screen readers do not announce the label for each field.
<input name="oldusername" size="20" value="tstuser" type="text" tabindex="1" class="mw-ui-input">
Should have id:
<input name="oldusername" id='"oldusername" size="20" value="tstuser" type="text" tabindex="1" class="mw-ui-input">