I have found the culprit - it's fixed for the next release.
Of course, it was a regex issue where -1 could match -10... All I had to do was to add a \b (word boundary) to make sure it won't match partial property id's (and I fixed the same issue for GTM too).
Thank you!

I already have a default code block inserted when creating a custom JS var, so I guess I could do the same for custom HTML tags (although a custom HTML might not contain any JS code... but that's not a big issue).

Yes, right - and there are other features that I might turn into view-specific (or property specific) features instead of globally applied.

I will gradually continue to improve the rich annotation feature so it will be possible to add a "status" annotation with a flag (icon/color) about anywhere you want.

I will double check this - the resulting regex is "99-99999-1(?!\\d)" which means the property id "not followed by a digit", so this should be prevented already.

I will see what is reasonably possible not to confuse users - also, wether the segment should be applied across all views, or just the specific one you are looking at (and then... what if the custom segment doesn't exist for some views, etc.). Simple things tends to quickly become more complex ;)

When picking segments, I could add a little "pin" marker to make those sticky, so you could actually have more than one segment always pre-selected. Would that work?

Hmm... just tried it... and you are right! Something must have changed in the UX.