Graphs of the OpenNMS instances stopped working after enabled storeByGroup. Specifically, the PS MarkSweep and PS Scavenge graphs are broken. I think this is due to the space not being properly escaped either by the graphing engine or the JMX poller not putting a \ before the space when inserting the entry into ds.properties.
The easy fix is to just rename the counter so that it doesn't have a space in it. We shouldn't be creating any files that have spaces in them anyway.