Steps to reproduce:

$oldLocation = $locationService->loadLocation( $locationId );
$locationCreateStruct = $locationService->newLocationCreateStruct( $newLocationParentId );
$copiedContent = $contentService->copyContent( $oldLocation->contentInfo, $locationCreateStruct );

var_dump( $contentService->loadContentInfo( $copiedContent->id ) );

MainLocationId is set to 0 in dumped content info