We've encountered this prob in production already. the issue is with Reader 9.x (where x < 4). The problem is resolved in Reader 10.
Reader 9.x doesnt seem to take into consideration that you've specified the locale to ENG on the field in designer.
The reason the rawValue is storing arabic is probably because your system locale is set to arabic, while your "regional" setting is english.
In control panel > Regional and Language Options > Administrative and see what the Language for non Unicode programs is set to.
Im assuming the arabic values is preventing you from validating with a RegEx.
You have 2 options.
1. Tell your user to upgrade to Reader X
2. write a function to convert the date (getTime) and the convert back and then do your validation.
A work around is to have them change the system locale to english if they have admin rights.