For me, this is a commonly seen error, and not just on 2005 coins. I usually think of it as 'ripped cheek'. I don't quite understand what happens to the obverse dies, but they obviously suffer damage, and this is the result.
I don't normally keep them but sometimes will if the cud (dot)is a lot bigger, which it occasionally is. There can also be small cuds in the 'rip'.
I'm not sure which denominations I've seen it on, but it's not restricted to just 20c.
It will take me a while to track down some of the ones I did keep and if/when I do, I'll put up some images.
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