This is a great question that I don't know the answer to....

This is a great question that I don't know the answer to. Generally you trigger a CGT event on the acquisition or disposal of an asset. In this case options were disposed and shares acquired. I can see the argument that the cost base and date of disposal/acquisition for exercised options into shares is the date of that exercise (and this agrees with the info I found on the ATO website). So even though there is no cash consideration (the capital gain is recorded in the value of stock acquired vs money paid) as such, the tax event is triggered.

If you think about it, an option is just the right to buy stock at a certain price before a certain date. So the market value of that option would be the difference in price between the market value of the stock the option gives you the right to buy, and the cost of exercising that right.

I don't suppose it's really any different from selling options you have in a company through the ASX and buying the heads in their place. That's definitely a CGT event.