Ann: Trading Halt-PIO.AX, page-203

This is completely wrong. The cost base of the original purchase (20k) is apportioned, so when you sold 20k worth or 20% you used 20% of the original cost base, so that 20k you sold would have a cost base of 4k and you've made a gross capital gain of $16k in the current year, the remaining 80k has a cost base of $16k, so if you realised it right now it would be a further gain of $64k.

The CGT regime is something every share investor should have a fundamental understanding of, knowing how it works can allow you to time trades with far better results. Based on the misinformation being spread in this forum I'd highly recommend that no one actually reads the advice here and that they both seek to educate themselves on the topic as well as seeking an accountant for advice on anything they're not sure of, if your accountant can't explain it so that you understand it then it's time to find a new accountant.