Zeppelin error 'Could not parse Master URL' on running spark notebook with new release

[swoehrl-mw]

I installed the new zeppelin package on a fresh AWS CloudFormation DC/OS 1.9 Stable cluster (with default settings) and tried to run the minimal example from https://github.com/dcos/examples/tree/master/zeppelin/1.9 .
After a few seconds it failed with status ERROR.
Investigating the interpreter logs inside the zeppelin docker container I found the following error:
org.apache.spark.SparkException: Could not parse Master URL: 'mesos://leader.mesos:5050'

Applying the changes from #1257 did not change anything.