Update - yeah it looks like all bids are automatically posted across all MtGox markets with MtGox handling the conversions - so all this speculation was wrong, sorry
But actually I could not find any announcement of that mechanism.
This is of course a pure speculation - but consider the facts. There is a bid wall for 20K BTC across all 15 or something MtGox markets for approximately the same price, even for currencies like NZD that did not see any action for a looong time. There used to be a similar 50K BTC wall across all markets - it started appearing somewhere in October I think (but maybe earlier) - it always was set in parallel for all markets (but I did not check this thoroughly until this week). The 50K wall from early this week at $2.4, across all markets would mean about 750K BTCs which means about $1.8 million. This could be from a crazy investor, realizing the scenario from the 'What would happen if someone invested a million dollars into bitcoins' thread, but if that is the case then why the 50K wall shrank to 20K wall simultaneously in all markets? This looks like a strange move if this was from an investor, but not that strange if it is a MtGox manipulation. It looks like they had a fund for this and after this fund was diminished by people selling into the bid wall yesterday they had to shrink the bid wall as well, it also looks that it is in fact just one bid wall leveraged across all the markets.
