Idea

The issue is that coupling nodes can have a flag that says whether they are to be preserved when you duplicate an object. This feature enables the references in a pasted object, such as Groups, ProcessFlows, etc. to be the same as the copied object.

The OnEntry listener for the Event-triggered Source is being preserved when you add the Processor to the User Library. The flag on that node is set to preserve the coupling. Adjusting that flag generally for all event listeners could potentially break something else.

To work around this issue, you can delete that listener node on the object in the user library.

Fixing the "bug" is complicated because it could affect other features that may expect that this coupling is preserved.

This bug wasn't marked low priority simply because of the amount of people it affects as you said. The amount of people affected by a bug is one criteria used when triaging bugs. Additional criteria include severity, complication, and ease of workaround. This bug has an easy workaround, does not cause severe data loss or crashing, and is complicated to fix, which could lead to causing other bugs if changed.