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hidden.platypus - If I had had your problem then I would be examining my work practices with respect to managing the downloading and installation of new versions of software.
For if the download for calibre 1.37 had been installing calibre 1.36 then there would have been far more than one person with the problem.
You can get an accurate picture of calibre usage numbers here ==>>
http://status.calibre-ebook.com/
No doubt Kovid could tell us exactly how many downloads there were of version 1.37, but by my reckoning, 1.3% of 23.3M is ~300,000+.
BR