Hi Ben,
I replied to your PM, but decided to also reply here to help anyone else that might have the same question. Some of you on this forum probably have more experience with this particular model than me, so please feel free to correct me if I've got anything wrong.
I believe this behavior is actually typical of these machines. Powcon (and most Workhorse) welders are actually not CC/CV, but Constant Power. This means that the "weld power" control actually controls the wattage, or heat, of the weld, rather than either current or voltage.
That being said, the GMAW-Short mode is particularly unique. It has a "Command Arc" feature built in, which senses the position of the welding wire via the arc voltage (the lower the voltage, the closer the gap) and as the wire gets closer to the workpiece, the current is increased until the wire melts and transfers to the workpiece. In this way, they accomplished a "short arc" weld without actually shorting (it's more like a low-power globular transfer process). This process is especially good for preventing burn-through on thin sheet metal.
Since neither the current nor voltage is being directly controlled by the "weld power" knob, it's difficult to predict what the voltage will be, especially in this mode. It really just takes a little bit of trial and error to find the best setting for your particular application.