Issue #32810: Jakben Imbel issues (sleep schedule breaking and incorrect vampirism stage)
When you accept the quest from the Gray Fox, Jakben will stop sleeping in the crypt between 6am and 6pm. This package was supposed to be reactivated when you have received information from the beggars, but the corresponding Journal Entry (25) is missing from the game. This causes Jakben's schedule to break and he will never go to sleep again.
and an extra possible bug:
Jakben has certain stage four vampire abilities such as Hunter's Sight and Embrace of Shadows. Strangely, he is a stage one vampire.
Both quotes taken from Oblivion:Jakben, Earl of Imbel (UESP).