Bug introduced in 8 or earlier and persisting through 11.3
The following behavior is stably reproduced with versions 8.0.4, 10.4.1, 11.0.1 and 11.1.1 on Windows 7 x64.
SetOptions[EvaluationNotebook, NotebookDynamicExpression :> Refresh[nb = EvaluationNotebook, UpdateInterval -> .1]]
Everything is as expected so far. Now just select the code
Dynamic[nb] and copy it via Ctrl+C. Here is what becomes:
nb you occasionally can get the hidden
This object isn't listed in
What happens here? From where comes the hidden
nb periodically switches between the two
NotebookObjects? Is it a bug?