Discering the trusmade is a pretty annoying quest alone please fix it there is no dialouge option to contiue the quest after returning the lexicon
PLEASE FIX !

...what? I completed the quest no problem.

Spelling corrections:

Discerning
Transmundane
Dialogue

Sorry about the grammar nazi moment there. Also I have not had any problems with the quest, care to share what bug your experiencing?

The wiki says there is a bug which can prevent the quest completing-

"After obtaining the Elder Scroll, if you immediately go to The Throat of the World and read the scroll then go to Septimus and give him the lexicon, the quest will say "wait until he has figured out the lexicon and then he will contact you". He never will, making the quest uncompleteable."

http://www.uesp.net/wiki/Skyrim:Discerning_the_Transmundane

If the game glitches so that you can't progress in the quest you can bypass it with a console command. I had this specific problem and I am testing it now to see if it really works, but I got the objectives to harvest the blood.