Q_DECLARE_INTERFACE() and Q_PLUGIN_METADATA(), interface id string need to match?

While studying the Plug & Paint Example, I read

By convention, we use a "Java package name" syntax to identify interfaces. If we later change the interfaces, we must use a different string to identify the new interface; otherwise, the application might crash.

How should I take the "...otherwise, the application might crash." statement?

Does it mean I should expect an application to crash if both, Q_DECLARE_INTERFACE() and Q_PLUGIN_METADATA(), identification strings are different?