https://trac.webkit.org/changeset/203030 regressed the feature to avoid re-generating JSON files when the cached JSON files contain up-to-date results.
This bug has been monkey-patched in the production server.
Created attachment 284055 [details] Fixes the bug
Comment on attachment 284055 [details] Fixes the bug rs=me
Committed r203486: <http://trac.webkit.org/changeset/203486>