Looking better at the manual, it will probably make more sense to just make a reference from the warning function to the error function, where the text describing this behaviour is long, detailed and includes two examples which probably would make little sense replicating.

So, I suggest that, after the first paragraph, ending with the words "makes sense for your program to go on.", a new short paragraph be added like this (no changeset, sorry):

If the warning message does not end with a newline character, Octave will print a traceback of all the function calls leading to the error.  See [error] for details and examples.

Like errors, warning do not produce a backtrace when the message ends with a  newline.

Unlike error(), this behaviour is not documented for warning().

It should be enough to copy and adapt the relevant text from the documentation of error() (look for "traceback messages").