Getting an Entry and saving the same entry wipeout the relations

By getting an entry and save it without do any changes or just the title wipeout the relations.

modify the title

$entry = ee('Model')->get('ChannelEntry')->filter('entry_id', 1)->first();
$entry->title = 'updated Title';
$entry->save();

do nothing, just update

$entry = ee('Model')->get('ChannelEntry')->filter('entry_id', 1)->first();
$entry->save();

This was a problem in EE2 (https://support.ellislab.com/bugs/detail/19817/relationship-data-getting-cleared-when-using-channel-entry-api) and it seems now also in EE3 as a problem.