The Hummingbird Performance Report suggests:
Install and configure a full page caching plugin like WP Super Cache or Batcache. This can substantially improve your response time for logged out visitors and search engine bots.
I am currently using Hummingbird to perform browser caching.
Is this a flaw, or does your caching plugin really suggest using another caching plugin? In which case, why does your performance plugin even have a caching option?