For example: https://todo.sr.ht/~nabijaczleweli/urlview-ng/8 says "Submitter: Leo L. Schwab", but the e-mail notification I got had "From: ~Leo L. Schwab".

The To: header in replying notifications is correct (or, well, isn't. it just never has a ~ in it, regardless of participant type. this is bug #2 probably, but who's ever read the To:?).

As further proof of concept, I (~nabijaczleweli)'m submitting this with From: наб nabijaczleweli/gaming@nabijaczleweli.xyz; and the issue will be recorded with "Submitter: наб", but our notifications will be "From: ~наб".