For example, if you make a button and set it to color on hover. If someone overrides those colors both for the initial and the hover state, in the Play mode the hover state uses the original color and not the one that was used to override it.
Usually if your layers have the same name, the changes you make in the editor will propagate to the other states in Prototype/Play mode.
For text layers you should rename them and type a generic placeholder name (such as layer: “label”, text inside it “label”) to assure your changes will be retained.
That said, the opposite is also valid. If you want a text from an instance to be immutable, just change the layer name slightly.