I'll copy this from below as its crucial

*** The turnoff of A0 must wait until after the button is released *** 
or the still-pressed button will retrigger the circuit.

_______________________

There's a fundamental problem with the circuit diagram AND there's 
almost certainly a problem with your circuit implementation.
Adding a pullup on A1 makes the circuit operation defined and this may 
have been specified elsewhere.

All Off

PNP = Q1
NPN = Q2
Upper diode = D1
Lower diode = D2

Button = ground diode junction on so PNP on so power on.
PIC pits A0 high so NPN on so PNP held on and all is well.

Now, A1 cannot either affect or see anything useful.
It is behind two opposed diodes so it cannot drive Q2_c hi or low

If A1 is input and Q2 is off then Q2_c is high but D2 blocks the Q2_C 
high so A1 see's a floating switch.
Pressing button changes A1 from float in to gnd in but this is not 
overly useful at this stage.

With Q2 on = power on then Q2C ~~= 0 volt so D1 cathode and D2 cathode 
are at float.
Again, closing button takes A1 from float to ground.
A pullup on A1 allows the button press to be seen and then the 
processor can turn power off using A0.
*** The turnoff of A0 must wait until after the button is released *** 
or the still-pressed button will retrigger the circuit.

_____________

With button open and no PIC then A1 *MUST* float. If it has a 10k 
pullup it must pullup. If it doesn't the cct is not as shown.

A P channel FET will work well as long as gate drive voltage is not 
too high or too low.


        Russell


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