Can confirm this is a bug and not intended. Reading the design myself and it looks like however it was written does not clearly specifiy for UI or QA how owned vs unowned skins should be handled. Likely the creator assumed people would understand to keep the current "show owned first then show unowned" - but in this new order being asked for.
Just a small miscommunication, not a monetization tactic. Skins are intended to be shown in all owned first, grouped together, then unowned.
Will be fixed next patch. Thanks!