For example conflict happend in builds
http://hudson.qa.jboss.com/hudson/view/DevStudio/job/jbosstools-nightly-3.1.0.M2/325/ and http://hudson.qa.jboss.com/hudson/view/DevStudio/job/jbosstools-nightly-3.1.0.M3/5 which led to compilation errors in tests component.
all that is related to code from common/buildRequirements.xml which uses return.properties as a marker that requirement was unpacked to clean-eclipse folder. So if one build unpacked requirement and put that marker in requirement definition folder, second just check that marker is presented and does nothing.