When I spoke to the Helpline about this a week or so ago, they said (I think) that I just need to deselect "At Market" and then reselect it to complete the order.
However, that didn't work and I got a message on the screen telling me something about the price stopping the change.
I should have taken a screen shot of that message.
WBC Price at posting:
$19.97 Sentiment: None Disclosure: Not Held
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(20min delay)