Prismatic Joint Position depends on Center of Mass

I initialize two actors and set their center of mass like that:

actor1 = thePhysics->createRigidDynamic(

actor1->setCMassLocalPose(physx::PxTransform(physx::PxVec3(0.295, 0.0, 0.0)));

actor2 = thePhysics->createRigidDynamic(

actor2->setCMassLocalPose(physx::PxTransform(physx::PxVec3(0.424, 0.0, 0.0)));

Than I create a prismatic joint between them:

physx::PxPrismaticJointCreate(*thePhysics, actor1, physx::PxTransform(0.0, 0.0, 0.0, physx::PxQuat(physx::PxIdentity)), actor2, physx::PxTransform(0.0, 0.0, 0.0, physx::PxQuat(physx::PxIdentity)));

If I start the simulation the joint position has in the first frame a value of 0.129 but the joint coordinate frames of both actors are exactly on the same position. If I don’t set the center of mass the joint position is 0.0 like I expect it.

Is there something that I do wrong? How I get the right value for the joint position?