PVS-Studio warning V669 for Micro-Manager

int pgFocus::GetOffset(double& offset)
{
  MM_THREAD_GUARD_LOCK(&mutex);
  deviceInfo_.offset = offset;
  MM_THREAD_GUARD_UNLOCK(&mutex);
  return DEVICE_OK;
}

Strange code. Most likely this is what should be written here: offset = deviceInfo_.offset;

This suspicious code was found in Micro-Manager project by PVS-Studio static code analyzer.
Warning message is:
V669 The 'offset' argument is a non-constant reference. The analyzer is unable to determine the position at which this argument is being modified. It is possible that the function contains an error. pgFocus.cpp 356

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