I had this happen too...the only thing I could think of was maybe I specified my dates incorrectly.  Like, if I put the vacation hold from, say sept. 1 to sept. 4, maybe it comes off hold ON sept. 4 rather than on sept. 5 as I wanted.  So, if it came off hold a day earlier than I wanted, people could request books from me.  Maybe this is what happened to you?

sorry for the double post, computer burp.

You're both right. If you put your shelf on hold and you had the only copy of a book, then I can add it to my wish list. When you take your shelf off hold, the book gets offered to me.

Vacation hold goes from the early hours of the first day you specify to the early hours of the last day you specify, so if you end it on 9/4, but you don't get home until that night, your account will be available for requests and wish list offers all that day and you might have some waiting for you when you get back. This shouldn't be a problem as long as you can login the day after you get back so you don't miss out on any 48 hour wish list offers.