Cast Academic Dispute. It makes the creature have to block. Then it asks if you want to "use the ability." So I hit no, assuming it was asking about reach, because not a single other Learn card has asked me that question. Then it didn't let me Learn, and it also didn't prompt me about giving reach. So I assume, if I hit "yes" that it would either give reach and let me learn together as one option, or simply never have the option of giving reach.
Nate W#03830 commented
Same here. Now I just always choose “yes,” but that isn’t ideal.
Happened to me as well.
Learning is still a may effect, but even if you choose to not rummage, and also not take any lesson from your sideboard, the game log would still show "[player name] learns". In case of academic dispute it does not happen, so for some reason, if you choose to not give the opponents creature (or yours ...) reach, you will not get to learn. Which is definitely a bug.
Why I use Academic Dispute and chooses No then I can't Learn
Same to me
Same happened to me. All other learn cards just open the sideboard and let you select the card you want from the SB or from your hand (to discard;draw) After castind Academic Dispute, the sideboard did not open, and I was prompted only to select yes/no to the cards ability in giving reach. I casted it in my own creature just for the learn, pressed NO because there was no point in giving it reach, and the Learn did function at all.