I have had no roboRIO experience yet, but, the cRIO control system outputs 5v through the red cable in the PWM by default(presumably for the use of speedcontrollers), but page 13 of the roboRIO manual says it outputs 6v there always.
However, if this was a real problem, it would have gotten caught in beta testing, and it wasn't. It is probably not the issue. As to what is, I couldn't tell you. Its definitely shorting with that kind of voltage drop.
Link to roboRIO manual
https://decibel.ni.com/content/docs/DOC-30419