Just goes to show you can't always trust simulators.

Golden rules:
1) - Place a 0.1uF capacitor across the Vcc and Vdd lines as close to the PIC as you can. If the PIC has 2 sets of supply pins use a capacitor across each set of pins
2) - Use a pull up resistor between MCLR and +ve.
3) - Tie all inputs to either +ve or GND via pull up or pull down resistors - typically 1K - 10K - Not advisable to leave inputs floating