I think it might be the "Allotment of Entitlements Shortfall and Placement". A couple of posters, Wubing and Kookaburra, said on that announcement thread that the extra shares would cause a bit of a flush in the market.
I'm kind of kicking myself that I'd missed seeing that before I bought .... never mind, I'm not too far down and OGX is going to be well worth it later on right??