Hi yanko,
i have no doubt that all is working fine ;-), what I wanted to say:
You can change the agent of the approval workitem via workflow administration.
Thats no big problem.
But if you do so, I think (i am not 100% sure) the new manager will not see this in his inbox and when he doesn´t see it, he can´t approve it.
Maybe it would be easier to use report RPTARQAPP in this case.
With this report you can approve leave requests, that woul be the easiest way, but then I think the user who executed the report will be the approver...