The "Buster Cannon 1" challenge seems to have two duplicate layers in the Collections menu, overlapped on top of one another. When you mouse over the challenge, the top one expands, but the bottom one doesn't, making the two layers clearly apparent.
This bug extends further than I initially thought. After earning the Firing Ma Lazer 3 challenge on the Squire, I came back to the tavern and checked my Collections, only to find that the double-layer effect had moved to one of the Pin Cushion challenges. Further investigation will continue.
I got a screenshot of it.