Error at decimal field display format (4.0)

When upgrading a German version of CRM 3.0 to version 4.0, a strange thing happened. All decimal, float or money fields behaved very strange.

Example: User enters a value 2. After clicking save button, the number changes to 200.00 and then immediately to 20.000.00.

Then I noticed that a decimal separator and a thousands separator were the same. Therefore I checked organization settings where everything looked fine.

The problem lied in user settings where both separators were set to dot (.)

SOLUTION:
Change must be made for each user. Set the decimal separator to comma (,).
Update the CRM database to affect all users: UPDATE UserSettingsBase SET DecimalSymbol = ','