This is a very simple bug to test: open up a Sencha Touch 2.2 app, then go into Chrome's developer console and type Ext.util.Format.dateRenderer('M d, Y')('2013-08-05')
The returned string is "Aug 04, 2013" when instead it should be "Aug 05, 2013." Any other date format seems to work properly (e.g. '2013/08/05' or '2013-8-5' or even '2013-08-05 ' with a trailing space). Only dates specified using YYYY-MM-DD are returned off by one. The format string (e.g. 'M d, Y') does not appear to have any impact.
Thank you for your report.
This is a known issue. The docs for the date method state that: