I'm thinking it might very possibly happen.
To build my SSCs, I recently ordered from monoprice crossover cables with a male and female connectors at either end. My plan is to cut off the male end and solder the female end to the SSC. Since I don't know where the "crossover" takes place (maybe the female connector?) I planned to test the wires and make any needed accommodations before soldering the wires into place.
So, I think your warning is a good one, and people should definitely test their pigtails before soldering and applying power.
btw, it was just after placing my order I saw that RJ has the pigtails available with the PCBs.