JavaScript Problem: Assignment to readonly property?

In Servoy 6.0.4 I have a warning telling me: Assignment to readonly property.

The code just sets a valid DB column with the value of a variable.
DB column is an integer and shows no difference to any other integer DB column (which doesn’t have this warning marker)

Any directions to what can solve this?

sounds like a bug, dataproviders should be assignable, do you have a testcase that you can put in a case?