[sayde]

Perhaps the answer to your question could help play into explaining exactly why Isshin sealed his shinigami powers away. Another thing worth mentioning is that Ryuuken seems to have just as many secrets and ulterior motives for some of his actions as Isshin does. Take for instance the issue you brought up. Even though Ryuuken helped Uryuu get his powers back under the condition that he stay away from Ichigo, you almost get the feeling that he had to know all along that Uryuu wasn't really going to obey that promise. I say this because Ryuuken has proven that he's an extremely smart and perceptive person (at least when it comes to matters regarding his son). He's great at predicting Uryuu's future motives, actions, and behaviors. So why make him promise in the first place if he already could assume the outcome? To test his resolve?

Whats more curious is that despite the promise he made Uryuu take, Ryuuken himself was obviously on somewhat friendly terms with Isshin for years--even after he discovered that Isshin regained his shinigami powers. So it begs the question as to why Ryuuken would push his son into staying away from shinigami while continuing to stay in contact with a shinigami himself.