telnetlib provides a low level interface to the telnet protocol.  The dialog you mention appears to be transmitted on the telnet connection, so it is unlikely there is any bug or missing feature in telnetlib that would affect your problem.

The sentence in the docs you appear to be referring to ("Do not reopen an already connected instance.") is just telling you that once you have used to telnetlib to open a connection, don't call open again.  It has nothing to say about a telnet connection made by some other program.

So, you have an application level problem and should seek help on the python-list mailing list or some other general help forum.  Unless you can identify something *specific* in telnetlib (bug or missing feature) that prevents you from solving your problem, I don't think there's anything more to be done here.

(As an aside, have you tried sending /r/n after the a?)