You don't hand in your passport when you are on bail, not unless it's made a condition of your bail which it only would be if there were significant concerns you'd abscond.
I completely take on board the point about the concern for the people of Kos. He'd have to sign on the sex offenders register here as he is now convicted but I don't think there are any legal provisions in place to enable them to be informed. That's clearly something that needs addressing and would benefit both countries.
In relation to his sentence, there is no legal provision to allow the judge to punish him (by refusing him his holiday) other than by sentening him and he's probably awaiting a probation report before he can do that.
I'm not saying it's right but on the basis of the limited information available the judge appears to have applied the law correctly.
I'm not morally in agreement with the decision, I'm just trying to explain why it's probably happened.