Created attachment 103872 [details]
If you have two selectors that match the same element and try to add that element to a region flow, no flow content displays in the region. The test file should display "A" in the region, but the second copy of the selector causes this to fail.
There's a missing openning brace after the second ".a". The bug doesn't seem to reproduce if I fix the test file.
.a <----- here
You are correct. I'd replicated the problem with multiple versions of the file, but they all must have had that typo that I missed.