Hey!
This is the current intended behaviour, a new tag will always override the state of an old one, so you'd want "<f=baseFont>1<f=newFont>2<f=baseFont>3" for this. I could add this as alternate behaviour in a future update maybe? I feel there was some reason I was avoiding it (I suppose it was because I didn't like the idea of needing closing tags, but I could still make that optional...? Or that this system technically runs faster since I never need to check which tag is closing, just override it with a null value), but with recent backend updates, it might not be that bad to add in now.