Your post is a little vague on so,e of the details pf what you are actually doing, but if I had to guess it sounds like you are buying from a sell order but setting the quantity higher than what was available at that price and setting a duration. That would explain why you said your buy range was set to that station. The result would be that you buy what is already available on sell orders at or below your price, and the remaining quantity produced a buy order with your risk in escrow until someone sells to it or your order expires.
You’re probably not going to experience many bugs, and can generally assume that when something strange happens in the first few months of play it’s generally going to be misunderstanding of the mechanics as you get settled. Forum’s always here to help.