It is because of your language parameter for your Oracle DB. They seem not to be the same for the 2 OS.
There are many parameters you can set to change language, number and date format in Oracle.
NLS_LANG: Global language
NLS_DATE_FORMAT: Date format
NLS_DATE_LANGUAGE: Date Language
... and much more ...
Read Oracle manual for details
Win32: Look in the registry
HKEY_LOCAL_MACHINE/software/Oracle to set parameters
Unix: Set corresponding env vars
Hth
JBL