Ann: Change of Director's Interest Notice, page-32

Not sure what industries you have worked in but I think you will find that for anyone who has a significant part of their remuneration paid in shares, "sell to cover" or selling a proportion of your holdings to cover the tax liability is pretty standard. Share based remuneration isn't taxed as PAYG but the tax man still wants his take at some point. You can easily check with other ASX companies or even have a look at the share trading of Scott Farquhar and Mike Cannon-Brookes if you want to see how CEO/Founders get liquidity to pay tax bills.