Sorry for the late reply.
It is difficult to show the issue in 2D but each time the merchant appears (after each level), they get lower in my playspace. The first time I looked down on them like I was quite tall. The second I was even taller (or further away) but could just reach the items to select them. By the third time (the video), I could not reach down to grab any items even when I got on my knees (I was hitting the physical floor).
I didn't see the same issue during the levels. I could still reach the bricks and weapons (although I wasn't sure what the harp did).