This is functioning as indented.Reader’s “Read Out Loud” feature only works with Static forms.This helps maintain the performance of dynamic forms that redraw themselves a lot.
However Dynamic forms do work with accessibility screen readers such as Freedom Scientific’s JAWS screen reader that use the MSAA (Microsoft Active Accessibility ) interface.
You can use JAWS to read dynamic forms. You just won't be able to use the “Read Out Loud” feature of Reader to test the "readability" of your accessible form. For that you'll need to use JAWS in your development cycle.