In interval mode the persistent YumCache is being cleared in rather cheap way (thanks me!) by checking if it's been longer than Chef::Config[:interval] since it was updated. The issue being when the interval (say 1 second) is shorter than the current ongoing chef run (mine takes ~18 secs right now) you end up with load_data being called multiple times. Doubt this situation would arise that much in production but it makes testing with a low interval pretty confusing.
The ideal would be to have a cleanup of it invoked at the end of the chef-client run, I'm just not sure how.