That kind of reminds me of the zij-hen-hun issue in Dutch; although completely unrelated, many people get it wrong: Native speakers commonly use hun (them, indirect obj.) instead of hen (direct obj., or ind. with preposition) (which isn't even considered wrong by quite a lot of people), or hun instead of zij (they), which is considered wrong though. I don't even get why they get it wrong
In Finland they are pronounced /di/ and /dem/. There are 300 000 native speakers of Swedish in Finland, and Swedish is an official language besides Finnish. "Finlandssvenska", the Swedish language spoken in Finland, is in many respects more conservative than "rikssvenska", Swedish spoken in Sweden.