diff --git a/engine/src/bullet/native/com_jme3_bullet_objects_PhysicsGhostObject.cpp b/engine/src/bullet/native/com_jme3_bullet_objects_PhysicsGhostObject.cpp
index b0c894472..e5bd4a394 100644
--- a/engine/src/bullet/native/com_jme3_bullet_objects_PhysicsGhostObject.cpp
+++ b/engine/src/bullet/native/com_jme3_bullet_objects_PhysicsGhostObject.cpp
@@ -183,8 +183,9 @@ extern "C" {
         {
             btCollisionObject *co1 = (btCollisionObject *)pair.m_pProxy0->m_clientObject;
             jmeUserPointer *up1 = (jmeUserPointer*)co1 -> getUserPointer();
-
-            m_env->CallVoidMethod(m_object, jmeClasses::PhysicsGhostObject_addOverlappingObject, up1->javaCollisionObject);
+            jobject javaCollisionObject1 = m_env->NewLocalRef(up1->javaCollisionObject);
+            m_env->CallVoidMethod(m_object, jmeClasses::PhysicsGhostObject_addOverlappingObject, javaCollisionObject1);
+            m_env->DeleteLocalRef(javaCollisionObject1);
             if (m_env->ExceptionCheck()) {
                 m_env->Throw(m_env->ExceptionOccurred());
                 return false;
diff --git a/engine/src/bullet/native/com_jme3_bullet_util_DebugShapeFactory.cpp b/engine/src/bullet/native/com_jme3_bullet_util_DebugShapeFactory.cpp
index 31a29b7a0..cbb95faa2 100644
--- a/engine/src/bullet/native/com_jme3_bullet_util_DebugShapeFactory.cpp
+++ b/engine/src/bullet/native/com_jme3_bullet_util_DebugShapeFactory.cpp
@@ -90,8 +90,6 @@ extern "C" {
     (JNIEnv *env, jclass clazz, jlong shapeId, jobject callback) {
         btCollisionShape* shape = (btCollisionShape*) shapeId;
         if (shape->isConcave()) {
-            fprintf(stdout,"Concave shape");
-            fflush(stdout);
             btConcaveShape* concave = (btConcaveShape*) shape;
             DebugCallback* clb = new DebugCallback(env, callback);
             btVector3 min = btVector3(-1e30, -1e30, -1e30);
@@ -99,8 +97,6 @@ extern "C" {
             concave->processAllTriangles(clb, min, max);
             delete(clb);
         } else if (shape->isConvex()) {
-            fprintf(stdout,"Convex shape");
-            fflush(stdout);
             btConvexShape* convexShape = (btConvexShape*) shape;
             // Check there is a hull shape to render
             if (convexShape->getUserPointer() == NULL) {
diff --git a/engine/src/bullet/native/jmeClasses.cpp b/engine/src/bullet/native/jmeClasses.cpp
index 254ef9d81..0d788e1e9 100644
--- a/engine/src/bullet/native/jmeClasses.cpp
+++ b/engine/src/bullet/native/jmeClasses.cpp
@@ -30,6 +30,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 #include "jmeClasses.h"
+#include <stdio.h>
 
 /**
  * Author: Normen Hansen
diff --git a/engine/src/bullet/native/jmePhysicsSpace.cpp b/engine/src/bullet/native/jmePhysicsSpace.cpp
index e3e566d4c..81c481f70 100644
--- a/engine/src/bullet/native/jmePhysicsSpace.cpp
+++ b/engine/src/bullet/native/jmePhysicsSpace.cpp
@@ -52,7 +52,7 @@ void jmePhysicsSpace::attachThread() {
 #ifdef JNI_VERSION_1_2
     vm->AttachCurrentThread((void**) &env, NULL);
 #else
-    vm->AttachCurrentThread(vm, &env, NULL);
+    vm->AttachCurrentThread(&env, NULL);
 #endif
 }
 
@@ -208,20 +208,28 @@ void jmePhysicsSpace::createPhysicsSpace(jfloat minX, jfloat minY, jfloat minZ,
 void jmePhysicsSpace::preTickCallback(btDynamicsWorld *world, btScalar timeStep) {
     jmePhysicsSpace* dynamicsWorld = (jmePhysicsSpace*) world->getWorldUserInfo();
     JNIEnv* env = dynamicsWorld->getEnv();
-    env->CallVoidMethod(dynamicsWorld->getJavaPhysicsSpace(), jmeClasses::PhysicsSpace_preTick, timeStep);
-    if (env->ExceptionCheck()) {
-        env->Throw(env->ExceptionOccurred());
-        return;
+    jobject javaPhysicsSpace = env->NewLocalRef(dynamicsWorld->getJavaPhysicsSpace());
+    if (javaPhysicsSpace != NULL) {
+        env->CallVoidMethod(javaPhysicsSpace, jmeClasses::PhysicsSpace_preTick, timeStep);
+        env->DeleteLocalRef(javaPhysicsSpace);
+        if (env->ExceptionCheck()) {
+            env->Throw(env->ExceptionOccurred());
+            return;
+        }
     }
 }
 
 void jmePhysicsSpace::postTickCallback(btDynamicsWorld *world, btScalar timeStep) {
     jmePhysicsSpace* dynamicsWorld = (jmePhysicsSpace*) world->getWorldUserInfo();
     JNIEnv* env = dynamicsWorld->getEnv();
-    env->CallVoidMethod(dynamicsWorld->getJavaPhysicsSpace(), jmeClasses::PhysicsSpace_postTick, timeStep);
-    if (env->ExceptionCheck()) {
-        env->Throw(env->ExceptionOccurred());
-        return;
+    jobject javaPhysicsSpace = env->NewLocalRef(dynamicsWorld->getJavaPhysicsSpace());
+    if (javaPhysicsSpace != NULL) {
+        env->CallVoidMethod(javaPhysicsSpace, jmeClasses::PhysicsSpace_postTick, timeStep);
+        env->DeleteLocalRef(javaPhysicsSpace);
+        if (env->ExceptionCheck()) {
+            env->Throw(env->ExceptionOccurred());
+            return;
+        }
     }
 }
 
@@ -235,10 +243,18 @@ bool jmePhysicsSpace::contactProcessedCallback(btManifoldPoint &cp, void *body0,
         jmePhysicsSpace *dynamicsWorld = up0->space;
         if (dynamicsWorld != NULL) {
             JNIEnv* env = dynamicsWorld->getEnv();
-            env->CallVoidMethod(dynamicsWorld->getJavaPhysicsSpace(), jmeClasses::PhysicsSpace_addCollisionEvent, up0->javaCollisionObject, up1->javaCollisionObject, (jlong) & cp);
-            if (env->ExceptionCheck()) {
-                env->Throw(env->ExceptionOccurred());
-                return true;
+            jobject javaPhysicsSpace = env->NewLocalRef(dynamicsWorld->getJavaPhysicsSpace());
+            if (javaPhysicsSpace != NULL) {
+                jobject javaCollisionObject0 = env->NewLocalRef(up0->javaCollisionObject);
+                jobject javaCollisionObject1 = env->NewLocalRef(up1->javaCollisionObject);
+                env->CallVoidMethod(javaPhysicsSpace, jmeClasses::PhysicsSpace_addCollisionEvent, javaCollisionObject0, javaCollisionObject1, (jlong) & cp);
+                env->DeleteLocalRef(javaPhysicsSpace);
+                env->DeleteLocalRef(javaCollisionObject0);
+                env->DeleteLocalRef(javaCollisionObject1);
+                if (env->ExceptionCheck()) {
+                    env->Throw(env->ExceptionOccurred());
+                    return true;
+                }
             }
         }
     }