Version 3.1 introduced an unwanted behaviour on checking partial paths on Unix. For example “/” would also hit “/var” if it was first in the list. So the “feature” (not a bug) of an exact match has now been added.
This means you don’t need to state the full storage name as a parameter, which makes it possible to use this service-check on a whole hostgroup in Nagios, i.e. check “C:” on all “windows-servers” in a single blow, while still allowing for exact matches on Unix-like systems.