Either use a 3rd-party markdown syntax or disable your 3rd-party CSS syntax(or file an issue to ask them to fix it). ST’s built-in syntax (Markdown) uses built-in scopes which 3rd-party syntax (CSS3, I guess) may not have.
This is almost certainly related to disabling the CSS syntax because you have the CSS3 syntax installed. The author of the CSS3 syntax recently cut a new release to fix this bug, so you may need to upgrade that package.
I’ve been experimenting with the “Hashed Syntax Highlighting” feature, and it’s really cool—in fact, I stumbled across this thread and as soon as I saw it, went and bought a ST license and started playing with syntax themes just so I could use that feature.
I do have one question though: is there any chance that
"background" will get support for hashed syntax highlighting as well as just
"foreground"? What I’m finding with HSH so far is that it’s hard to make the colours bright enough that the feature is useful while still not being overwhelming, not drawing too much attention away from other parts of the file, and keeping enough contrast to make things readable.
Because the background has a larger “surface area”, so to speak, than the foreground, I’m thinking it might present an opportunity to make the colour muted enough that it doesn’t grab attention and/or keep the text dark enough that there’s enough contrast to be readable, while still being noticeable enough that the feature is put to good use.