I’m afraid there’s no simple fix for this - Anki uses Apple’s text editor to handle this, and it appears to be including the surrounding newline (“div”) when you select text that way.
Spaces and newlines are represented differently internally, which is probably why Apple’s web libraries are behaving differently in the two cases. It’s possible that the situation will improve if/when AnkiMobile adopts the move to BRs that the latest computer beta has, but it is not something I’ve had time to explore yet.