Both of these scales will produce that 'minor major seventh' chord, by using the notes contained therein, and 'stacking thirds'. That's not a problem. That's exactly what will happen!
In most minor keys, expect any notes from the three minor scales to pop up. That means in Am, for example, A B C D E F F# G G#. So, now, it's possible to also have a more common m7 - A C E G, as opposed to A C E G#. In fact, the classical melodic minor scale notes means both chords can be made using just the notes from that scale.
Think of theory more as guidelines, and explanations of what might happen, rather than any rigid rules. Yes, there's an ambiguity there, if you like, but if that mM7 can be used in a minor piece, bear in mind that that minor piece could be from any of the minors. There's nothing anywhere to say otherwise, or even to say 'thou must keep to one set'.