Contribution Net Amount does not fill in automatically when Additional Details section is expanded

When entering a Contribution with just the basic fields in view, the Non-deductible Amount and Fee Amount fill in automatically with $0 and the Net Amount fills in with [Total Amount - Fee Amount]. However, if the "Additional Details" section is expanded to show these three fields, only the Non-deductible Amount is automatically completed. It isn't a much of a problem when the Fee Amount is left null, but when the Net Amount is left null upon saving the Contribution, this is incorrect and can cause problems with searching and reporting. (i.e. a search for Net Amount > 10 will not return the expected Contributions.)

What is especially confusing about this is that there are two different behaviors for the field: 1) the Net Amount is automatically filled in unless 2) the Additional Details section is expanded, so typical users are likely to expect Net Amounts are accurate for all contributions, not just for contributions that have a fee amount.

Is there even any reason why Net Amount is an editable field? In what case would it not be Total Amount - Fee Amount?