Headings: sentence-style capitalization

[helene-spring]

I'm getting some warnings I can't figure out from Google.Headings:

  54:5  warning  'Optimizing for writing:          Google.Headings 
                brainstorming' should use                            
                sentence-style capitalization.                  
 70:5  warning  'Optimizing for reading:         Google.Headings 
                eye exam' should use                            
                sentence-style capitalization.                                 
 93:4  warning  'Libraries and physical       Google.Headings 
                infrastructure' should use                      
                sentence-style capitalization.                  

I have no idea why these headings are considered to not have sentence-style capitalization. They are simple h2 or h3 headings in .mdx files. Here's a snippet around one of these headings:

to give you control over this balance.

### Optimizing for writing: brainstorming

For large ...

so I don't see any flagrant problem here. Here is the contents of my vale.ini:

[*.{md,mdx}]
BasedOnStyles = Vale, Google, write-good
Vale.Spelling = YES
Vale.Terms = NO # Enforces really harsh capitalization rules, keep off
dictionaries = en_US
CommentDelimiters = {/*, */}
# Disable very noisy style rules:
Google.Contractions = NO
Google.Parens = NO
Google.Passive = NO
Google.We = NO
write-good.E-Prime = NO
write-good.Passive = NO
write-good.TooWordy = NO
# Don't Vale links:
BlockIgnores = \]\((?:https?|mailto):[^\s)]+?\)
TokenIgnores = </?(?:Steps|Step)\b[^>]*>
TokenIgnores = </?(?:CodeGroup)\b[^>]*>

I managed to suppress these warnings by swapping out $sentence in .vale/styles/Google/Headings.yml with a regex. So I figured I would go to the source and see whether we could avoid local fixes by figuring out what's going wrong here.