When you say “flow pane” do you mean you have the domain object selected and you’re clicking on this button?
Those aren’t panes. Whichever of those buttons you have selected is the smoke sim object type of the selected object. If you click on Flow there, you’re not switching planes. You’re changing your object to a Flow type instead of a Domain type. The buttons below that row change contextually based on the object’s type, so it then shows Flow options instead of Domain options. You’re creating a smoke sim with two Flow Objects and no Domain. It then doesn’t hold any of your new settings because you’ve created a broken simulation without a Domain to hold it.
Again, reading the manual would serve you better than a popup dialog. You want a warning when you try to put a flow type on a Domain object, but that’s impossible. Domains don’t have flow types. You cannot possibly change the flow type of a Domain object. You have to actually change the object to a Flow object first, which is what you’re doing.