I don’t think that’s correct - URLs with # work fine here (DT 3.8.3), e.g. try selecting some text from this URL and it will include the full URL fine: python - How can I do multiple substitutions using regex? - Stack Overflow
I think what’s happening is that there’s some hardcoded logic for Discourse forums (or just for this Discourse forum) - I’ve also seen it with clipping PDFs where @cgrunenberg confirmed it is hardcoded behavior: Set preferred width when capturing PDFs - #10 by cgrunenberg
TBH I don’t think exceptions like that should be hardcoded, but then again as you say: there might be some other reasoning in play here too.