This is basically a Plexus thing because
DefaultPlexusContainer from plexus-container-default:1.0-alpha-9-stable-1 is using
File.toURL() instead of
File.toURI().toURL() when populating the class realms from local JAR files (e.g. the resulting URLs return illegal characters like spaces).
The latest plexus-container-default seems to already use the proper methods so this issue is more or less a request to incorporate this fix into the 2.0.x branch. For instance, usage of Ant 1.7 is severly affected by this (
MANTRUN-68).
Fixed by updating to recent Plexus versions.