Steps to reproduce this behavior:

1. Moderator Alice views a topic.
2. Alice elects from "Quick-mod tools" the "Move topic" options.
3. Alice clicks "Submit".
4. In the meanwhile moderator Bob has successfully deleted the topic.
5. For Alice /includes/mcp/mcp_main.php is running check_ids() which doesn't find the topic (any IDs) anymore, hence the function just returns FALSE.
6. The code enters switch ($mode) and since there is no mode, Alice gets a NO_MODE error message.

However, this results in an unexpected error although we (the code) know(s) better.

To cure this I did the following in that file:
Find

trigger_error('NO_MODE', E_USER_ERROR);

Before, add:

if( $quickmod ) {

	switch( $action ) {

		case 'lock':

		case 'unlock':

		case 'make_announce':

		case 'make_sticky':

		case 'make_global':

		case 'make_normal':

		case 'make_onindex':

		case 'move':

		case 'fork':

		case 'delete_topic':

			trigger_error( 'TOPIC_NOT_EXIST' );  // no E_USER_ERROR

		break;

		case 'lock_post':

		case 'unlock_post':

		case 'delete_post':

			trigger_error( 'POST_NOT_EXIST' );  // no E_USER_ERROR

		break;

	}

}

This way moderator Alice does not have to encounter an error which looks like something of the board broke.