The bugged "crystal" marking seems to be fixed on stallions (report from live is here https://www.horsereality.com/forum/topic_95548/irish-cob-part-of-white-marking-vanishes-in-stallions).

However, the whites on the mane dosen't cover entire area as it does on foals:

Link to stallion: https://beta-v1.horsereality.com/horses/3741925/foal-doe-3741925