Why doesn't the pull-up work on DTR input?

XBee & XBee Gateway XBee - Zigbee
, ,
1

I have an XBee3 module (through hole) with default settings and 1006 firmware. D8=1 (DTR/SleepRQ). PR=FFFF and PD=FFFF (i.e. all pull-ups enabled). The problem is that pin 9 (DTR) is floating.
What am I missing? Is this a bug?