The increment/decrement on the max chars field configuration allows a max value of 999 while any value is accepted if the user types into the field.
Also, the maximum characters that can be used in a form (according to the known limitations document) is 80 fields of 255 chars each or equivalent. There is no validation while the developer is configuring the fields but for the run-time error that is hard to debug. Can not a validation be added when the fields are configured rather than at run-time?
-Varun.