The issue is currently in production.
Steps:
- As a user who can edit Special:ManageMentors go to the page and click Edit for any mentor, e.g. https://en.wikipedia.beta.wmflabs.org/wiki/Special:ManageMentors/edit-mentor/6768
- Click "Is away?" checkbox. The suggested date/time will be displayed with the clear button, x(<span class="oo-ui-iconElement-icon oo-ui-icon-clear"></span>) placed at the end of the suggested string
The clear button should be placed at the end of the text box as it's done for, e.g. Search text box input: