Date constants in zend are determined from sniffing out locale in this order (form zend_locale comments)
1. Given Locale
2. HTTP Client
3. Server Environment
4. Framework Standard
I'm thinking the difference between the two systems is going to be reflected in the Server Environment.
To correct and avoid this problem in the future you can specify the locale options within your application.ini using these configuration directive.
resources.locale.default = <DEFAULT_LOCALE>
resources.locale.force = false
resources.locale.registry_key = "Zend_Locale"
The locale should be set to a string like en_US
Zend_Locale specificly sniffs the locale from the environment from a call to setlocale and parsing the results.