Mine has nothing to do with newly minted coins, I don't even mine, been waiting since last night.
It doesn't matter what you do with your bitcoins.
All the bitcoins that get deposited into Mt Gox get dumped into a single pile.
Some of the coins are dumped in there by miners, whose coins can not be spent until 100 blocks after they were mined.
Some of the coins are only spendable if a Mt Gox employee grabs the private key out of safe or something.
The software Mt Gox uses to choose which coins to spend when customers want to withdraw bitcoins is apparently suboptimal.
If their software tries to spend a coin which has not matured (>100 blocks since being mined), the entire transaction ends up in limbo.
Another possible problem is that some transactions end up with too many inputs with an insufficient fee the transaction also ends up in limbo.
If a withdrawal transaction fails, Mt Gox has to double spend those inputs before trying the withdrawal again because otherwise there's a possibility the original transaction will suddenly get mined and they will irrevocably pay out twice.
