When you change the resource no. in a job planning line, the entire line is 're-validated': for instance the quantity is defaulted back to 0.

This can be very inconvenient when you just want to change the resource but keep the planned hours:
i.e. the job planning line is initially created as a budget when the actual resource has not yet been defined: the actual resource will be filled in later.

Please change the re-validating of the job planning line, or make it optional (via a message/question) whether or not to default the quantity back to 0.