Unitialized motion vector information is used during the boundary strength derivation on the encoder side leading to encoder/decoder mismatches. The xGetBoundaryStrengthSingle() function assumes the motion vectors of refIdx < 0 blocks have the value 0.

e.g.

xGetBoundaryStrengthSingle()
.....

        if ( ((piRefP0==piRefQ0)&&(piRefP1==piRefQ1)) || ((piRefP0==piRefQ1)&&(piRefP1==piRefQ0)) )
        {
          uiBs = 0;
          if ( piRefP0 != piRefP1 )   // Different L0 & L1
          {
            if ( piRefP0 == piRefQ0 )
            {
              pcMvP0 -= pcMvQ0;   pcMvP1 -= pcMvQ1;
              uiBs = (pcMvP0.getAbsHor() >= 4) | (pcMvP0.getAbsVer() >= 4) |
              (pcMvP1.getAbsHor() >= 4) | (pcMvP1.getAbsVer() >= 4);

.....

If piRefP1==piRefQ1==NULL and piRefP0 == piRefQ0 && piRefP0 != NULL, motion vector information of P1 partition is used in uiBs derivation.

following patch should address the issue