Write the smallest test program you can which demonstrates the issue. In 
particular, remove the mysql dependency and see if you can replicate the 
problem. Then you can either eliminate or show that mysql is the cause 
of the problem.

As far as I can see here, strftime works the same on both:

$ ruby -v
ruby 1.8.6 (2007-09-24 patchlevel 111) [i486-linux]
$ ruby -e 'puts Time.now.strftime("%Y-%m-%d %H")'
2010-05-11 13
$ ruby19 -v
ruby 1.9.2dev (2009-07-18 trunk 24186) [i686-linux]
$ ruby19 -e 'puts Time.now.strftime("%Y-%m-%d %H")'
2010-05-11 13
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