Why is XB s2 destroyed when LED is attached to DO1 and set high?

I send an API packet to a breadboarded XBee S2 to set pin 19 / DIO1 high. To verify, I have an LED connected to that pin. I also have an LED connected to pin 15 / Association. When I apply power the Ass’n LED lights, then blinks. No problem. When I send a packet to turn on DIO1, that LED turns on. Within seconds the 3.3V regulator in a chip (TO-220 package) gets hot and the XBee gets hot and so I disconnect power. The XBee never works again. I’ve put in a 2k ohm resister on both pins. Doesn’t help. What could be the problem? I’ve gone through 7 XBees so far.

Note: the regulator is outputting a bit under 3.65 V. I tried swapping another new identical regulator. It does the same. When I first used these regulators a few days ago, I recall them putting out 3.33 V on the dot. Something strange going on with that also.

The output voltage that the DIO lines can support on an XBee ZB module is 1.2V max. They can also only source up to 40mA total with each line supporting no more than 1 to 2 mA of current.