Subscriptions Block is rendered with an empty form as authenticated user

I please need help for further investigation.
The form bulding function in subscruotions_ui.module correctly returns NULL or array() (depending on the case) but the drupal_get_form() functions always render the form so that the block finally receives the empty form HTML and renders it.

I'm now using the following quickfix to hide the block content if the form array has no "account" key (which would always be present for a proper form) and set the block value to NULL to hide the block entirely:

In custom module:

/**
 * Implements hook_block_view_alter().
 */
function MYMODULE_block_view_alter(&$data, $block) {
  // Fix empty form block for registered users on pages without permission to subscribe to.
  // See: https://www.drupal.org/node/2496435
  if ($block->module == 'subscriptions_ui') {
    if (!empty($data['content']) && $data['content']['#form_id'] == 'subscriptions_ui_node_form' && !isset($data['content']['account'])) {      
      $data['content'] = NULL;
    }
  }
}

What we'll need is a solution to tell drupal_get_form() not to render the form if the form function returns an empty array or NULL. Alternatively we could pre-check the result of the form building function not to be NULL to pass the form array to the block. But that would require us to execute subscriptions_ui_node_form() twice?

The problem is between subscriptions_ui_node_form(), drupal_get_form() and subscriptions_ui_block_view() in subscriptions_ui.module.

Yes the affected content type IS marked as static content!

Well that is possible but does not change anything about the bug behind.

What ever this is, we should fix it. Where would you suggest to put the issue?
I had no other module with this issue yet.