Same thing for me. I put (based on hovering), "They plant the new book in certain", which I knew was going to get a red flag, because... well... that completely doesn't make sense. I was totally thrown back by "They reserve the new book". That's way off! I'll take galaxyrocker's advice and report...
Heavens, that didn't make sense, but I think it does now.
Had I known "in áirithe" meant "in reserve" basically, it would have made much more sense ahead of time, given that, syntactically, the manner of time is always described at the end of the sentence. Gach maidin, gach oiche, go minic, etc.
To me, "they put the new book on hold" means that the publishers have postponed the launch of the new book - chuir said an leabhar nua ar an méar fhada.
Having said that, if it was used in a question, "Could you put that on hold for me?" does make sense as a request to keep a copy for me until I come back later for it, but it actually has the implication that the item is in stock already but it's not convenient for me to take it right now (or I don't have the money!) , where as I would ask "Can you reserve that for me?" if it wasn't in stock yet, but is expected in soon.
I understand, but even in the library, I would only ask them to put something "on hold" if it was already on the shelf, and I wanted them to set it aside for me so that someone else didn't get it before I could call by and pick it up, whereas I would ask them to reserve it for me if they were waiting for someone else to bring it back.
And I wouldn't say "they have the book on hold for me", I'd say "they are holding the book for me".
I think the main issue is that the exercise is framed as a statement, not as a question, and the phrase "put something on hold" means to temporarily pause a process. That can include temporarily pausing the normal process of giving a book out on the usual first-come-first served basis, but cuir in áirithe has a different meaning, and wouldn't be used for other things that are typically "put on hold", like phone calls or business plans.
What it comes down to is that if "they put the book on hold for me" is how you would say "they reserved it for me", then that's a valid translation into your idiolect, but cuir in áirithe doesn't mean "put on hold" generally.
(It's also worth nothing that the NEID entry for "reserve" differentiates between "hold back"/coinnigh/coimeád and "(to) book"/cuir in áirithe)
Maybe it's just a matter of where you live. I live in Toronto (Canada.) I can go on my library's website to find a book I want and put it on hold (it could be at a different branch and they'll send it to mine, or they could all be out and when one comes back in, they'll notify me by phone or email and then I can go and pick it up.) In any case, I now have a better understanding of what the Irish means, so it's all good.