Sorry, I again misinterpreted HaChu's scoring. Which was indeed such that there was no mate in 16, but that the checks could only be kept up for 17 moves. So you are probably right about the Flying Ox/Whale copying mistake. The MSM clearly depicts a Flying Ox in the diagram for this tsume puzzle, though.
My guess is that the designer did not anticipate the Flying Ox's diagonal move being problematic, rather than it being a copying error, since the kanji for the Ox and Whale are vastly different. Of course, what's important is that the problem is fixed and solved.
Not sure if you still update the hgm.nubati site anymore, but feel free to further discuss this problem in the MSM Errata B if you want (If you do, I'd recommend having a picture of the position).
P.S. I've updated the Applet, deleting the MD problems and solutions and adding B23, as well as citing our comments for B23's source (the MSM citation is already covered by the MSM Series B citation).
My guess is that the designer did not anticipate the Flying Ox's diagonal move being problematic, rather than it being a copying error, since the kanji for the Ox and Whale are vastly different. Of course, what's important is that the problem is fixed and solved.
Not sure if you still update the hgm.nubati site anymore, but feel free to further discuss this problem in the MSM Errata B if you want (If you do, I'd recommend having a picture of the position).
P.S. I've updated the Applet, deleting the MD problems and solutions and adding B23, as well as citing our comments for B23's source (the MSM citation is already covered by the MSM Series B citation).