Sounds better than "I traded it on another site". At least with this one, it sounds like a mistake was made or the system has a glitch, and the book will probably be posted later.

They probably meant to post it to their TBR and accidentally posted it to their bookshelf instead.

You should ask them if they will repost it to you once they are done with it.

My guess is that when they received the book from PBS they had it added their bookshelf on hold. Then they accidentally unheld the book.   I've done that before myself. I normally don't put them on my bookshelf on hold. 

I got one awhile back that was "I can't mail it because my sister is reading it."  I think that some people just don't realize that a book is WLed and they don't expect it to be ordered so soon.

I've done that before. Unless you uncheck the box, it goes on hold on your bookshelf when you receive a book. I didn't realize and put my shelf on hold when I went on vacation. Took it off hold when I got back and everything came off hold, including all the books I had received, not yet read, but forgot to uncheck the box for. I felt bad turning down the WL requests, and I was so confused. Now I am sure to always uncheck the box.

What?  If I understand you correctly, if I use vacation hold and when I return and turn off vacation hold, all the books on hold on my bookshelf will become available?  All the books I receive that I intend to repost after I've read them are on hold on my bookshelf.  Vacation hold will turn that off?  What a nightmare.

I could see it as being an honest mistake. I've almost clicked on a book at times to unhold it when I didn't mean to.  If the book was WL & accidentally posted, then it would automatically go to someone's book queue.

Hopefully someone else will offer you the book or he/she will again when the book is ready.

if I use vacation hold and when I return and turn off vacation hold, all the books on hold on my bookshelf will become available?  

There are two kinds of 'hold' that can affect your bookshelf - vacation hold and putting individual books on your bookshelf hold. If you come off vacation hold, those books that you have on hold individually should still be on hold.

Edited for correction - sorry for any confusion. When I originally typed this I was thinking 'bookshelf' but typed 'wishlist'.

I come on and off vacation hold regularly and have NEVER had a book on my TBR/hold post itself incorrectly.

Ending a vacation hold should not effect books that are on individual hold on your bookshelf.  To take a book off individual hold, you have to "post" it, and confirm that it meets the golden rule.

I got  "the dog ate it"... i'm not joking.

Having 2 dogs-I can believe that one.

For the person using the Bookshelf hold feature when they go on vacation: every time you do that, all your books go to the back of the FIFO line.  It's better to use the Vacation option and then autorequest any WL books in which you are near the top of the line.

I can also believe the dog ate it. My newest cat is cardboard chewer and just took off the corner of a borrowed book :(

My dog loves adhesives - I have to keep her away when I'm wrapping books because she tries to eat the packing tape.

Once I saw her nosing around on a library book and didn't pay much attention - but later, I realized that she had lifted up the dust jacket on the inside back cover and eaten a hole, maybe an inch and a half in diameter, clear through the cover. Not at the edge of the book, either - away from the edge but still underneath the dust jacket. I think she was after the glue.

I took the book back to the library and showed them what happened, but since the hole was completely hidden under the cover they decided it was perfectly usable and they didn't even charge me a fine - which really surprised me!

Two common reasons given for sender cancelling a transaction:  The puppy chewed on it, or the kids spilled Kool-aid on a stack of books.

I think the one I've had to use most often is "I put it down on something wet in the kitchen." Those damn counters...

I sent one down next to a box of babywipes one time not realizing that a wipe had gotten caught under the cover and was haning out. (white wipe agains white container).  The book spent the night sucking all the liquid out of the wipe like a sponge.

OH - just want to correct what I wrote above. I totally forgot about this. I didn't know about vacation hold at the time, I just did "check all" and hit hold. (I realized soon after that I lost my place in FIFO for all of my books!)

But my point was that it could have been an honest mistake, such as when I did it completely unknowingly.