Hi pawczu. This is just another chesslarious moment. I do have Shredder and a PC. Runned the position you gave for 2:20 minutes at Depth 30! The mate it shows is in two moves, not one. You are completely right, Qxh3#. Chesslarious! (So, your Mac is not the problem 
this time)
Shredder for Mac cannot find mate in 1!
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Hi,
I am using Shredder to do my post game alaysis and recently found interesting position in which Shredder for Mac cannot find mate in 1 (without any strength limit). If you have Shredder for PC, can you please check it out?
FEN:
2Q5/5p2/5K2/7k/8/7p/8/8 w - - 0 1
It should give Qxh3# but it does not!