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I often copy an existing Panel file as the new Panel looks quite similar. However, if you copy that file into another package ate least existing tooltip-text references into local bundle files cannot be resolved any more. Unfortunately the error occurs at runtime. Reworking all that occurrences manually does help, but a complete refactor run would be helpfull.
You can try to use the automatic internationalization (can be turned on for new GUI forms, or for texts not internationalized yet). It could behave better with the refactoring. Even if it does not, it can be temporarily turned off before the refactoring, which puts all strings back to the java file, then turned on after, which moves the strings to the actual bundle file again.