Symptoms
Decimal values aren't processed correctly between SmartForms textbox and the underlying SmartObject.
It doesn't matter what Format I'm using (German / US number Format, use user Settings). The result is the same.
Diagnoses
Some user account settings do not have the correct Regional Settings
Resolution
After changing the Regional Settings for the Default user and K2 Service Account and logged in user to English (US) and doing an IISRESET and restarting K2 HostServer Service, it was working and values return correctly in SmartForms.