This bug appears to result from an integer overflow in the piety scheme, allowing the PC to have extremely positive or extremely negative piety.

How it works:

Either:

1) Pray approximately 1700 times in a row (this requires some preparation to deal with divine retribution, but nothing that cannot be overcome). After these prayers, the PC's piety will wrap around from negative to extremely positive, allowing multiple (pre)crownings and essentially unlimited prayers for healing, food etc.

2) Sacrifice a several hundred million gold on an altar. This will send the PC's piety into the stratosphere, but with a sufficiently large amount, the PC's piety will collapse into negative values.