In G4MuonMinusCaptureAtRest::AtRestDoit, there is an uninitialized variable
which results in crashes and incorrect results:

  if( G4UniformRand()*(lambdac + lambdad) > lambdac) {
    // Decay
    pEMCascade->DoBoundMuonMinusDecay(targetCharge,mass,&nCascade,Cascade);
    // Generate secondaries from capture
  } else {
    DoMuCapture();
  }
  aParticleChange.SetNumberOfSecondaries( nGkine + nCascade );

In the above segment of code, if the program branches into the
DoBoundMuonMinusDecay section of the if, the variable nGkine is not
initialized, and can have a huge negative value when used in the call to
SetNumberOfSecondaries.

The line:

nGkine = 0;

should be inserted after the call to DoBoundMuonMinusDecay to fix the problem.