Compact does not release space to the system with WiredTiger

The documentation clearly claims that "On WiredTiger, compact will rewrite the collection and indexes to minimize disk space by releasing unused disk space to the system." However as far as I can tell in 3.0.7 this does not actually happen. I reduced dataSize of a collection from 130 GB to 30 GB and the storageSize remained the same at 61 GB after running compact. This was mentioned in SERVER-19062 which was marked as a dup for a ticket that doesn't address this problem.