I encountered a case where the encoder generated a bitstream containing a +32768 coefficient level when sign hiding is enabled.
After some debugging, the code responsible is located inside the function xRateDistOptQuant() of TComTrQuant.cpp.
Relevant code (lines 1988-2000):

          if(piQCoef[minPos] == 32767 || piQCoef[minPos] == -32768)
          {    
            finalChange = -1;
          }    
     
          if(plSrcCoeff[minPos]>=0)
          {    
            piDstCoeff[minPos] += finalChange ;
          }    
          else 
          {    
            piDstCoeff[minPos] -= finalChange ; 
          }     

Adding a printf after the first 'if' block:

printf("xRateDistOptQuant: minPos=%d plSrcCoeff[minPos]=%d piQCoef[minPos]=%d piDstCoeff[minPos]=%d finalChange=%d\n", minPos, plSrcCoeff[minPos], piQCoef[minPos], piDstCoeff[minPos], finalChange);

I got the following output (for a DC coefficient):

xRateDistOptQuant: minPos=0 plSrcCoeff[minPos]=20059 piQCoef[minPos]=124277 piDstCoeff[minPos]=32767 finalChange=1

As a result, the second 'if' adjusted the coefficient level to +32768 which got placed into the bitstream.

Two possible solutions:

1. Add saturation to [-32768, +32767] for piDstCoeff[minPos] after the second 'if' block.
2. It's very likely that the first 'if' is wrong and piDstCoeff should be checked instead of piQCoef. A similar piece of code can be found in lines 969-981 of the same file.