In some projects, JavaFX being one of them, NetBeans will force you to do manual ”Clean and Build” to compile instead of simply having it compile on save. Changing this property from the GUI (Project > Properties) doesn’t always seem to be possible. The solution is simple – in your project.properties, change this
compile.on.save.unsupported.javafx=true
to
compile.on.save.unsupported.javafx=false
project.properties is located in /[Projectfolder]/nbproject