Exclude site from search works very inconsistently

I often get many results from a single page when doing searches, and I don't always want results from the predominant page, but when I try to exclude it, the site pops up all the same:

I initially noticed it with twitter in July, and I assumed it was because of the domain name change to x, but even when excluding both twitter and x, I'd get search results from the site.

This should probably be a separate search ticket, but the operator '=' no longer seems to work as an equivalent for "". I'm including this bit of information because the exclusion operator is also a special symbol: '-'

The expected behavior is for sites excluded with the syntax -site:abc.com to not appear in search results