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When on-wiki JavaScript fails JSMin's (JSParser to be exact) validation, it makes the minified script file just throw an error.  This error thrown includes the page name (e.g. User:Example/common.js).

This output is cached, which means if someone copies the JavaScript (e.g. to debug the problem), it will show the wrong filename/page name for that subsequent user.

This usually won't be too hard for a user to figure out (particularly if there's only one copy).  However, the page name could be added to the cache key to fix this.  I don't think this will have too much of a performance impact.  There generally shouldn't be many identical copies of a script (there are certainly scripts widely imported, though).