It seems that Fieldx is NOT a calculation field, but rather a field with an auto-entered calculation. Change the field's type to Calculation - it will be automatically set to unstored and recalculate at every window refresh.
Thanks. Making the field a calculation gives updates. I guess that's
the main difference between the two methods. A "Calculation" field
must always update itself whereas a field defined otherwise but
containing a calculation may not. Your answer is the solution.