Extremely reproducible by rolling "/roll 1d4!pro<1" and "/roll 1d12!pr<10" a couple of times. On the d4 roll you'll get [0+1] occasionally with the 0 being rerolled. This shouldn't happen, Penetration should only subtract 1 from the results of rolls that would be added to the initial total, not any dice rolled after the first. There is definitely a problem with this interaction, even if I'm wrong about the specifics due to the obfuscation of the penetration math.
