see: #16730
**
Reproduce the issue**
Take any calendar field, for example administrator/com_content/models/forms/article.xml
Modify the field "publish_up" like this, i.e. add the attribute todaybutton="false"

<field
	id="publish_up"
	name="publish_up"
	type="calendar"
	label="JGLOBAL_FIELD_PUBLISH_UP_LABEL"
	description="JGLOBAL_FIELD_PUBLISH_UP_DESC"
	class="inputbox"
	translateformat="true"
	showtime="true"
	size="22"
	filter="user_utc"
	todaybutton="false"
/>

Open an article for editing and go to the publishing tab.
The calendar has no todaybutton, but the clear button has gone with the today button.
So the user cannot change a selection in the calendar.

Additional Information:
This behaviour is coded in calendar.js, but seems somehow awkward.