Problem 2510

G4OpBoundaryProcess tests for very short step lengths. If the step length is shorter than the geometrical tolerance, it is the volume reallocation step after one of the reflection-type boundary interactions (i.e. the particle is going back into the same volume it came from). The status is set to StepTooSmall, and the code returns (after setting velocity).
https://geant4.kek.jp/lxr/source/processes/optical/src/G4OpBoundaryProcess.cc#L186

However, occasionally the step length is greater than the geometric tolerance (1e-9 mm). In this case the status is not set to StepTooSmall. The example LXe has code to check for this. 
https://geant4.kek.jp/lxr/source/examples/extended/optical/LXe/src/LXeSteppingAction.cc#L168

This results in a JustWarning exception (see it with LXe.mac, maybe increasing the number of particles). 


G4WT4 > step length: 2.10214e-09
G4WT4 > LXeSteppingAction::UserSteppingAction(): trackID=1498 parentID=871 opticalphoton E(MeV)=2.43451e-06n/ at (-79.9805,-0.685051,-126.228) prePV: Cladding1 postPV: Fiber
G4WT4 > 
-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : LXeExpl01
      issued by : LXeSteppingAction:
LXeSteppingAction: No reallocation step after reflection!Something is wrong with the surface normal or geometry

*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------