Thanks. Now I get something different, related to the hits:
<pre>
(gdb) up
#1  0x00002aaaab202400 in edm::RefCore::pushBackItem(edm::RefCore const&, bool) ()
   from /afs/cern.ch/cms/sw/ReleaseCandidates/vol1/slc5_amd64_gcc481/cms/cmssw/CMSSW_7_1_X_2014-03-27-0200/lib/slc5_amd64_gcc481/libDataFormatsCommon.so
(gdb) up
#2  0x00002aaad92f253e in edm::RefVectorBase<unsigned int>::pushBack (this=0x2aab0db3fe80, product=..., key=@0x7fffffff616c: 0)
    at /afs/cern.ch/cms/sw/ReleaseCandidates/vol1/slc5_amd64_gcc481/cms/cmssw/CMSSW_7_1_X_2014-03-27-0200/src/DataFormats/Common/interface/RefVectorBase.h:53
53            product_.pushBackItem(product, true);
(gdb) up
#3  0x00002aaad92ef61f in edm::RefVector<edm::OwnVector<TrackingRecHit, edm::ClonePolicy<TrackingRecHit> >, TrackingRecHit, edm::refhelper::FindUsingAdvance<edm::OwnVector<TrackingRecHit, edm::ClonePolicy<TrackingRecHit> >, TrackingRecHit> >::push_back (this=0x2aab0db3fe80, ref=...)
    at /afs/cern.ch/cms/sw/ReleaseCandidates/vol1/slc5_amd64_gcc481/cms/cmssw/CMSSW_7_1_X_2014-03-27-0200/src/DataFormats/Common/interface/RefVector.h:65
65            refVector_.pushBack(ref.refCore(), ref.key());
(gdb) up
#4  0x00002aaad92ee195 in reco::TrackExtraBase::add (this=0x2aab0db3fe80, r=...)
    at /afs/cern.ch/cms/sw/ReleaseCandidates/vol1/slc5_amd64_gcc481/cms/cmssw/CMSSW_7_1_X_2014-03-27-0200/src/DataFormats/TrackReco/interface/TrackExtraBase.h:23
23          void add( const TrackingRecHitRef & r ) { recHits_.push_back( r ); }
(gdb) up
#5  0x00002aaad93119be in RecoTrackAccumulator::accumulateEvent<edm::Event> (this=0x2aaae65cb940, e=..., iSetup=..., tracks=..., tracksExtras=..., hits=...)
    at /afs/cern.ch/work/g/giamman/fastsim/mixing/CMSSW_7_1_X_2014-03-27-0200/src/FastSimulation/Tracking/plugins/RecoTrackAccumulator.cc:109
109             NewTrackExtraList_->back().add( TrackingRecHitRef( rHits, NewHitList_->size() - 1) );
(gdb) list
104           //dummySeedRef ) );
105           NewTrackList_->back().setExtra( reco::TrackExtraRef( rTrackExtras, NewTrackExtraList_->size() - 1) );
106           // rechits:
107           for( trackingRecHit_iterator hit = track.recHitsBegin(); hit != track.recHitsEnd(); ++ hit ) {
108             NewHitList_->push_back( (*hits)[hit_counter] );
109             NewTrackExtraList_->back().add( TrackingRecHitRef( rHits, NewHitList_->size() - 1) );
110             hit_counter++;
111           }
112
113           track_counter++;
</pre>