i can see if you're a store that sells playmobil, how you can get in trouble for selling custom sets if it's out of the same store. Because Playmobil wholesales the merchandise to the stores, meant to be resold at retail and in their original form.
If a store owner (be it online or in real life) has access to wholesale parts, customizes them, and then sells them along side stock playmobil toys from the same store, it's a bit of a conflict of interest because, essentially, you'd be selling second-hand toys that dont' meet playmobil standards along side the brand new stock toys that do, and out of the same store. Customers may confuse the customs for actual Playmobil stock toys, or riding off Playmobil's marketing (meant for stock playmobil toys) in order to sell their customs, thus, using Playmobil to promote your non-endorsed customs.
That seems to be the common theme between this Malta lawsuit and the other (unless they're one in the same?): the customs are being sold by vendors who also sell stock playmobil regularly, and out of the same venue. Maybe this can be avoided if the customs were sold out of a seperate and private venue not associated with the vendor's store that carries playmobil.