Sumac handling of nested args: internal state not reset when arg is changed

[AustinBGibbons]

Experienced by labs framework when modifying nested rtc directly, instead of the underlying client.

Sumac maintains state for args which is not reset after the field is changed.

[squito]

More specifically -- when first parse() is called, then field references are changed, and then runValidation is called (as is done in labs & other frameworks), runValidation is still using holding onto references to the old objects from the arg fields. It should re-acquire all the field values again.