Hot Plug-in debug on RL78 - cannot stop execution

Question

I'm trying to enable hot plug-in debug option on RL78 MCU by setting the HPIEN bit in the corresponding option byte.

When I attach the E1 debugger to the running target, I can use Live Watch to inspect the RAM variables, however, trying to break the execution results in "can not compulsory break" error message:

The test software I'm trying to debug is a simple infinite loop incrementing a variable, toggling a pin and servicing the watchdog:

volatile long i = 0;

void main( void )
{
  hpi_initialize_prog();
  PM8_bit.no5 = 0;
  while (1)
  {
    i++;
    P8_bit.no5 = i;
    WDTE = 0xAC;
  }
}

Did anyone manage to use breakpoints / step through the program using the hot plug-in debug?