Filtering by custom tags returns wrong results

When applying filters in Sentry you get some odd results that do not seem to match the filter exactly.

For example if I search by a custom tag (server_name) in this case, I get results matching the server_nam, but also results without the specified server_name.

This only seems to happen without custom tags, other filters like is:resolved or level:warning all work fine. I’ve tried looking through JSON responses from the REST API endpoints to see if actually underwater the server_name is the same value somehow, but they are just as expected like they are in the web interface.

Is there anything I’m missing when I’m searching for tags?