They've done that to me several times. I'll place an order for 300k and they give me 5k for openers. It's almost as if they're waiting to see if you'll change your order. I can understand it when you're buying on the bid, but not the ask. But having seen it numerous times, I've concluded that what is happening is the mm for my broker (tda) doesn't have the shares available, so what he does is give the 5000 shares to lock in the commission, then he goes to the mm with the shares and gets a chunk with which to fill the order. For example, I see blocks on the T&S that are generally larger than my order when mine gets filled. That tells me that they are bundling orders for tda rather than doing them individually. That happened with almost every order I placed yesterday.
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