How to prevent Drupal from scrolling to the bottom of ajax-appended content in a form
You could override the Drupal.ajax.prototype.success handler (/misc/ajax.js) in your theme  to control behavior, maybe commenting out Drupal.unfreezeHeight(); and Drupal.freezeHeight(); could do the job?
Just copy the whole function and manipulate it your own way.

/**
 * Handler for the form redirection completion.
 */
Drupal.ajax.prototype.success = function (response, status) {
  // Remove the progress element.
  if (this.progress.element) {
    $(this.progress.element).remove();
  }
  if (this.progress.object) {
    this.progress.object.stopMonitoring();
  }
  $(this.element).removeClass('progress-disabled').removeAttr('disabled');

  Drupal.freezeHeight();

  for (var i in response) {
    if (response.hasOwnProperty(i) &amp;&amp; response[i]['command'] &amp;&amp; this.commands[response[i]['command']]) {
      this.commands[response[i]['command']](this, response[i], status);
    }
  }

  // Reattach behaviors, if they were detached in beforeSerialize(). The
  // attachBehaviors() called on the new content from processing the response
  // commands is not sufficient, because behaviors from the entire form need
  // to be reattached.
  if (this.form) {
    var settings = this.settings || Drupal.settings;
    Drupal.attachBehaviors(this.form, settings);
  }

  Drupal.unfreezeHeight();

  // Remove any response-specific settings so they don't get used on the next
  // call by mistake.
  this.settings = null;
};


Another option would be to render the ajax form with ajax_commands where you could add custom js handlers to your callback.