I’ve not fully debugged it, but you’re not the first to experience this, and it seems like some themes are able to counter it, like Minimal and GitHub themes. Surely others are able to counter this, but those are the ones I’ve used which eliminates the problem.
It would be nice to have this addressed at a higher level, not sure if it qualifies as a bug or what, but if one wanted to make a bug report one would need to follow the bug report template and reproduce the issue in the Sandbox vault for starters.