hopefully this resolves #1558 for good

Author: ptrthomas

karate-core/src/main/java/com/intuit/karate/core/ScenarioEngine.java

@@ -1930,10 +1930,12 @@ public Variable call(Variable called, Variable arg, boolean sharedScope) {
             case JAVA_FUNCTION:
                 return arg == null ? executeFunction(called) : executeFunction(called, new Object[]{arg.getValue()});
             case FEATURE:
-                // will be always a map or a list of maps (loop call result)
+                // will be always a map or a list of maps (loop call result)                
                 Object callResult = callFeature(called.getValue(), arg, -1, sharedScope);
-                recurseAndAttach(callResult);
-                return new Variable(callResult);
+                synchronized (runtime.featureRuntime.suite) { // make sure any artifacts from a callonce / callsingle are handled
+                    recurseAndAttach(callResult);
+                    return new Variable(callResult);
+                }
             default:
                 throw new RuntimeException("not a callable feature or js function: " + called);
         }

karate-core/src/test/java/com/intuit/karate/core/parallel/parallel-outline-1.feature

@@ -7,10 +7,10 @@ Background:
  * def data = [ { name: 'value1' }, { name: 'value2' }, { name: 'value3' }, { name: 'value4' } ]
  # java object that comes from a callSingle in the config
  * def helloClass = HelloConfigSingle
-* callonce read('call-once-from-feature.feature')
+ * callonce read('call-once-from-feature.feature')
 
 Scenario Outline:
- # * call read('called.feature')
+ * call read('called.feature')
  * match functionFromKarateBase() == 'fromKarateBase'
  * path 'fromfeature'
  * method get