Extensible Flexfields - Form Rules and Validation Rules issues

Summary:

Hi All
I'm working on the additional assignment information page
I've tried using a form rule with no conditions to hide an Extensible flexfield, but it didn't work.
I've also tried using validation rules based on these same Extensible Flexfields just for testing an error Message, but neither worked.
It appears that the Form Rules and Validation rules don't apply to Extensible Flexfields.

I've built the same kind of rules based on Descriptive Flexfields, and they worked correctly. Has someone built rules based on extensible flexfields? Is there something different to consider?

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