You're right about the value of the shares, but not about the tax break.
If I go onto CommSec right now, and sell the shares I have, I'll get a certain amount of money. Even if I try to buy in before I sell, my order goes to the end of the queue - they'll sell to the first person in the queue, not to me.
In pre-open, you can play games like that, but you're gambling that it'll come out the way you want. So there's no point in selling and trying to buy back; you'll get the capital loss, but not the shares, unless you're really lucky.
Also, the tax office frowns at selling and buying back in just to dodge tax; if there's a bit of a break between the sell and buy-back, okay, but if it's at the same time, you're likely to have problems should you be audited.
That said, I fully concur that $20k worth of shares being sold is not a cause for concern. I wouldn't worry until we see six or seven figures' worth traded, and I don't expect to see those volumes until after the company makes its next announcement.
(I was going to rant here, but I don't see the point. It's blatantly obvious that those who need the message drummed into their skulls are wilfully ignorant, and I can do without the stress.)
Disclaimer: I am not a tax accountant. Do not rely on this comment without checking to see if it's (a) correct, and (b) applicable to your position.
DMN Price at posting:
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