The org.activiti.engine imports org.joda.time.format package It can be resolved from org.apache.servicemix.bundles.joda-time bundle or from joda-time (via other path – org.apache.servicemix.bundles.drools and org.apache.servicemix.bundles.xstream.
Because the org.apache.servicemix.bundles.xstream bundle imports optional org.joda.time.format in version [1.6.0, 3.0.0) and is installed with activemq feature in featuresBoot the package is resolved with version 1.6.0 from joda-time which is also part of the activemq feature.
Next when installing the activiti feature, the org.activiti.engine requires the same package with higher version [2.1.0, 3.0.0). With the refresh option we had probably no problem and org.apache.servicemix.bundles.xstream would be probably resolved again with the package from org.apache.servicemix.bundles.joda-time in higher version which is also allowed for org.apache.servicemix.bundles.xstream. But with refresh disabled it doesn't happen and the package can not be correctly wired into org.activiti.engine
This problem didn't happen with ActiveMQ 5.9.0, because the activemq features includes org.apache.servicemix.bundles.xstream with version 1.3_2 which imports org.joda.time.format with range [0.9,1). Because the import is optional and no bundle provides this package with this version, the package is not wired into org.apache.servicemix.bundles.xstream and org.activiti.engine imports the package from org.apache.servicemix.bundles.joda-time
ActiveMQ 5.9.1 feature includes org.apache.servicemix.bundles.xstream with version 1.4.7_1 which imports org.joda.time.format with version provided by joda-time which is not compatible with import in org.activiti.engine