#validate and #submit ignored if button handlers are defined

I don't know if this is a bug or feature, but I spent the better part of a day trying to track down why my validation hook was never being called. Originally spotted in D7.14, but the code is exactly the same in the 8.x branch.

The function form_execute_handlers() first checks to see if the handler type is defined for a button press, and if so proceeds to ignore the #validate and #submit handlers defined on the top-level form element. According to the FAPI docs, it sounds like the #validate and #submit handlers should always be called.

Logically, it seems like the form-level handler should always be invoked and any specialized submit handlers should be added to the handler chain...

Is there a reason this:

  // If there was a button pressed, use its handlers.
  if (isset($form_state[$type . '_handlers'])) {
    $handlers = $form_state[$type . '_handlers'];
  }
  // Otherwise, check for a form-level handler.
  elseif (isset($form['#' . $type])) {
    $handlers = $form['#' . $type];
  }
  else {
    $handlers = array();
  }

should not be something like this?

  $handlers = array();

  // If we have form-level handlers, add those
  if (isset($form['#' . $type])) {
    $handlers += $form['#' . $type];
  }
  // If there was a button pressed, add its handlers
  if (isset($form_state[$type . '_handlers'])) {
    $handlers += $form_state[$type . '_handlers'];
  }

That code's been in there since waaaay back when, so not sure if there was a reason it was structured that way. However, if a contrib module adds a validate handler on a submit element, it causes every handler set on #validate or #submit to be skipped, which can't be a good thing...

Ran into it with the revision_scheduler module on D7 specifically, but there's nothing keeping other contrib modules from doing it as well.