The blend control affects the volume in bypass with trails on.  From a circuit point of view, that's because it is muting the input to the reverb but still blending the reverb output with the analog dry signal.  Musically, it means your dry signal maintains the same level with the reverb on or off.  However, since we have a blend control instead of a reverb level, that does mean a loss of volume with trails on.  The effect is most noticeable with the blend at more than 50% wet.

In true bypass mode (trails off), the signal level is not affected when the pedal is bypassed.  You can switch modes by removing the bottom plate and adjusting the trails switch.