Capital letter in lists seems random

Given the following list in markdown:
```markdown
- make sure the conditions are met
- deal with simple cases first
- lists are good
- the adjustment is still linear
- the origin is not like with...
```

Harper (0.36.0) will detect a capitalization issue with the first and last entry only. I have no idea what's the rule here.

Edit: reproducible with 0.37.0

Reproduce the markdown list example with Harper 0.36.0 or 0.37.0 and inspect how capitalization is reported for the first and last entries. Trace the list-capitalization behavior and confirm the finished change applies a consistent, documented rule to all five entries.

Written by the indexing model from the issue text.