Ok i see the problem here, and the issue is a bit deeper and more complicated..
When you change a tree in any way from the tree-configuring screen, TFLM knows this, and when you try to quit it will prompt you to save your changes, abandon them, or cancel the quit.
When you change a tree node text item from the main screen (which is what i think you are doing given the text you quoted), it assumes this is something you just want to change temporarily. i.e. it *assumes* that by changing it here and not in tree configuration screen that you do *not* want to save it, that's why it doesn't prompt you.
I can see why some users would prefer it this way and some would prefer to be able to make changes that will get saved here.
One way to solve the problem is add an option about whether changes made on main screen should be treated as changes to the tree that presumably should be saved (and thus user will be prompted if they try to change tree or exit without saving them).
This would match up well with adding an option to do the same thing with changes to variables, which I was also asked about the same thing.