I just discovered several books on my wish list on hold.  I have no memory of putting them on hold, I'm not even sure I was aware I could. (I knew the feature was coming, I don't remember noticing it was here).

Several of the on-hold books are alternate versions of one I was just offered. I know I didn't go in since it was offered and put them on hold.

Did it do this automatically?  When did this start?

There's this thread about it: http://www.paperbackswap.com/forum/topic.php?t=192360

Seems that it's a new feature that came with the WL expander feature.

It started doing that a few months ago when the put the individual hold feature on teh WL.  It's to prevent further offers for the book while you have one pending.  Then if the book goes lost or times out you can just unhold the other versions. 

It does not delete them for you when you receive one though.  I know I've seen on here that it's supposed to ask you if you want other versions of a WL book deleted when you mark one received-but I've only been asked this once in 2.5yrs.