Yeah, it is a bit weird, and I know at least Pro Tools doesn’t do it.
My hunch is that some designer or programmer figured “well, if there’s no previously written value there’s no automation to trim” and then decided to have it just be touch/latch instead for the first pass. It definitely makes much more sense to simply write an automation value offset based on whatever the current value happens to be even if it hasn’t been written as automation yet.
So yeah, I agree with you.