The issue is caused by oversimplified parameters parsing implementation in this class: https://github.com/jenkinsci/groovy-plugin/blob/master/src/main/java/hudson/plugins/groovy/Groovy.java

        //Add groovy parameters
        if(parameters != null) {
            StringTokenizer tokens = new StringTokenizer(parameters);
            while(tokens.hasMoreTokens()) {
                list.add(Util.replaceMacro(tokens.nextToken(),vr));
            }
        }

I would suggest to switch to org.apache.commons.exec.CommandLine.parse(..) method from Apache commons-exec.
Not ideal, I know, but probably the best possible option if parsing command-line is inevitable.

Is anyone interested in the patch? It would be very straightforward.