I noticed this too, but thought it was just my misunderstanding as a noob.
I purchased new because I am down to only a few "market calls" and don't want to run through them before the first game day is over (and six other days left in the week), not finding the right fit every time I looked, even with hundreds/thousands in Sale and Storage.
Initially, I thought the market call was in place to limit players from hogging used aircraft during the game. Since there is no limit, other than funds, to the number of aircraft one can purchase, it did not seem that a new purchase would / should logically limit a used purchase. But, I see the message that I have already made two orders on the used market screen.
Actually, I only did one purchase of two aircraft. So, per the wording of the message, I technically have not placed two orders.
Rather confusing this all, and rather artificially limiting at the very start of the game - both this two order limit (combined used/new) and the market call mechanism, especially on the very first day when everyone is starting with the same funds, naturally limiting their ability to acquire more than a few aircraft, while several hundreds or thousands of aircraft sit in Sale and Storage status (for a few aircraft that is more than could be purchased if everyone maxed out on any one of them - given the player limit).
Probably better off letting everyone just pick any two aircraft they can afford that are initially available on the first day and be done with it, with these rules engaging after the first day ends.