[Mark McLeod]

The 8-slot's collect metal dust and debris inside.
If it's a used one, have you cleaned out the case lately?
It should be cleaned each year before being mounted on a new robot.

It does weird things when there is dust inside, so that might be a possible cause.

I assume nothing else is plugged into the Analog ports that might cause a short.

You can test the Breakout with a multimeter to see the battery voltage on the pins you put the jumper on. Measure from the pin to any ground.
Use the multimeter to verify continuity through the jumper in case it isn't really a jumper. (I only say that because I once found a team using a cable connector instead-it didn't work.)