Not getting preferred maps in ranked matches

Hi there! Since the last update, I've been getting less and less matches in the map I have set as "Preferred Map" and more of just any random map that I haven't banned. I just played 2 seconds of Megarandom before my opponent resinged without playing. I asked why he quit if he had chosen the map and he said that he hadn't. Is this the way it is supposed to be? Two people each choosing a preferred map and getting a third one that no one chose? Is it that it sets a map that neither chose when we have banned each other's preferences?

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The in-game chat, basically saying that neither one chose Megarandom