What I mean is:
[Sat Sep 11 03:04:38 2010] You begin learning from this codex.
[Sat Sep 11 03:04:46 2010] You no longer have your active codex item in your inventory and cannot continue learning from it.
[Sat Sep 11 03:04:59 2010] You begin learning from this codex.
[Sat Sep 11 03:05:12 2010] You no longer have your active codex item in your inventory and cannot continue learning from it.
[Sat Sep 11 03:05:33 2010] You begin learning from this codex.
[Sat Sep 11 03:05:40 2010] You no longer have your active codex item in your inventory and cannot continue learning from it.
and so on, and so on, and so on.
And NO, I did not move around anything between those messages.
EDIT: after some research, Glyphs seem to deactivate whenever you move an item in your bags, loose a buff, get a buff, or get hit by any spell whatsoever, including NPC's nuking you.