I had both the RTL Design and Netlist Design open, and used the text editor to modify a source file. The RTL Design displays the yellow banner indicating that the view is out-of-date, but not the Netlist Design.
Should both of them not go out-of-date for a source file change?
The RTL design and Synthesis Run go out-of-date when the source code is modified.
The Netlist Design does not go out-of-date as it remains in sync with the synthesis run on disc. If you run synthesis again, the Netlist Design is marked out-of-date.