My client birth-date is reverting to the year 1900
With several users in Australia and one in Canada (and a problem that was quite common in Europe 7-8 years ago).
That DOB problem is usually fixed by changing your windows short date format settings to mm/dd/yy. Go in to the Windows date settings and tell it very specifically what you want the "short" date to be.
If this does not resolve the problem submit a support ticket and include the following information:
The version of Windows you are using?
Is it happening on existing clients or new clients?