zk flag fails when specifying a file and the replicated logs

The zk flag supports referencing a file. It works when registry is in_memory, however in a "real" environment it fails.

the following starts up just fine.
/usr/local/sbin/mesos-master --zk=file:///etc/mesos/zk --registry=in_memory

however when the follow is executed it fails:
/usr/local/sbin/mesos-master --zk=file:///etc/mesos/zk --quorum=1 --work_dir=/tmp/mesos

It uses the same working format for the zk flag, but now we are using the replicated logs. it fails with:
I0723 19:24:34.755506 39856 main.cpp:150] Build: 2014-07-18 18:50:58 by root
I0723 19:24:34.755580 39856 main.cpp:152] Version: 0.19.1
I0723 19:24:34.755591 39856 main.cpp:155] Git tag: 0.19.1
I0723 19:24:34.755601 39856 main.cpp:159] Git SHA: dc0b7bf2a1a7981079b33a16b689892f9cda0d8d
Error parsing ZooKeeper URL: Expecting 'zk://' at the beginning of the URL