Problem with form caching and #after_build

There seems to be some conflict with the way that entityconnect_cache_set() is used and the use of #after_build.

If I have an #after_build callback that adds a custom submit handler to the entity connect add button it doesn't work. My submit function never gets called.

If I move that code directly into the form alter function it works OR (and the issue lies somewhere in here) if I comment out the line

<?php
  entityconnect_cache_set($cache_id, $data);
?>

in the entityconnect_add_edit_button_submit() function then my code in the after build does work and my submit function does get called.

So there is something funny going on in relation to the use of that cache it seems.