What did you override the expression with? What is the base expression? I just did a quick test and it worked, so I think either the instance expression must be somehow marked as overridden, but with an empty expression.
And I don’t quite understand what you mean when you say that you’re deleting the base expression… wouldn’t this result in the instances having a blank expression (unless they were overridden, of course), which would in turn lead to this error? (Note: the error, end of expression, char 0, is caused by an empty expression value)
Regards,