Not sure what you mean by ' unreliable when pulled low' but the connection from A2 to the relay driver transistor needs a resistor. As you have it, A2 tries to go to 5 volts but the emitter base junction clamps at 0.7 volts. A2 may deliver up to 25 mA or the excess load may reset A2 to 0 volts. That may be causing internal problems with the PIC. Try 1-5 k ohms between A2 and the base.

HTH
Brian