Someone's advised me that Spotify might be inheriting bugged language behaviour from your browser's language settings, even if your browser itself isn't typing backwards. I've run all other pending system and program updates (not including any changes to Spotify itself) and it seems to have stopped it. Might be a coincidence, but might be worth a try.
This is still a bug. It's pretty clearly a behavioral bug in how the cursor focus works in the search box. If you start typing and type too quickly, the cursor keeps pinning itself to the left side of the search box between each letter, and you end up with eimaj instead of jamie If you type at a much more deliberate speed, it works fine. So, if you put a slight pause after you type that first character in the box, it should work fine.
Of course a) people don't naturally do that, if they are experienced typists who know what they want to search for (lots of people, lots of the time) and b) this is a solved problem in literally every other app with a search box that gets cursor focus by default. Come on, Spotify Mac team, you can lick this one!