If you click in the field, a value gets suggested.
Clicking on the "x" seems to remove the value.
If you click outside of the field, e. g. to go to the next field, the value gets re-established in the field.
Clicking on "x" should remove the value and the field should be left blank unless you click in the filed again.
Observedin PF versions 3.8, 3.9.3.
It does work as expected in PF 3.5.1
All are using MW 1.31.. The sandbox example uses PF 3.9.3 and MW 1.34