Internal pull-up resistors not working on some pins.

[BluCode]

I have recently been experimenting with the internal pull-up resistors in terms of waking from deep sleep, and I have found that the pull-up resistors on pins 4, 12, and 13 are not working. I measure no voltage with a meter when the pull-up *should* be enabled, and the same meter measures about 3.1V on the other RTC pins. I have not tested the pull-ups on non-RTC pins.

Is this intended? Is there a workaround?