calendar control formats date in dd/mm/yyyy in debug mm/dd/yyyy otherwise

I've noticed that when in debug the calendar control on my page formats its date in dd/mm/yyyy format but when operating the page normally the date gets formated in mm/dd/yyyy (as is intended).  I don't have the culture specified in config.web so am expecting that it is set to the default culture="en-US" so was expecting the date to always be mm/dd/yyyy in debug or otherwise.
Can someone tell me how to stop this from happening?  It makes debugging difficult when working with date issues,
Thanks much in advance, Roscoe         
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