Besides the fact that you need a favor just to do it. I advocate to leave it in because it isn't fair that some sons stay in court and others leave for a holy order when you order them to take the vows. I think there is something based on their traits or stats that determines it but it of course isn't clear to you ahead of time. Its frustrating to prep a son to be a Prince-Arch-Bishop of a duchy only for him to join the Templars. And where previously it had no fix, now with a gift and a favor you can invite him back he is still celibate and good to go.
The fact that some stayed was due to them being married and the divorce action making them go home instantly. Should be fixed in 2,5,2 though, unless there are additional issues.
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