Commerce search index matches wrong category

Description

Steps to reproduce

Note: The below steps aren't verified. Thay are based on experiences in a different catalog:

1. Use Quicksilver with the default catalog.
2. Create a new category in Fashion, next to Mens, which shares the same prefix in the code, e.g., "mens" and "menstuff".
3. Create some products in the new category.
4. Reindex.
5. Go to the mens category

Expected:
Only products in the category are included.

Actual:
Products are mixed from both categories.