I think I have a solution for the problem:
Comment these lines in maxigallery.php
Line 577
//handle image in gallery folder
//$newname = $mg->getFilename($name);
//if(rename($mg->path_to_gal.$name, $mg->path_to_gal.$newname)){
// $handleMessage = $mg->handleFile($newname, $modx->db->getRecordCount($rsx));
//} else {
$handleMessage = $mg->handleFile($name, $modx->db->getRecordCount($rsx));
//}
...
Line 591
//$filesExist[$newname] = ’valid’;
Try it. Hope it will help!