I was tipped to this issue by a reader, and after a similar question was raised on MobileRead Forums I decided that this was worth a post. Here's the notice that has appeared on some library websites:
Important notice for Kindle Users:
The Kindle book format has been temporarily disabled from this website.
OverDrive is referring to the close integration they have with Amazon. Normally this would enable library patrons to transfer library ebooks to their Kindle, but it is broken at the moment.
Here is OverDrive's explanation:
Below is an update on the issue reported to you early today regarding some Kindle users may be prompted to ‘Buy now with 1-Click’ when attempting to download a Kindle book from your OverDrive-powered website, rather than being taken to a page to redeem their checked out eBook title. Unless the user wants to buy the title, they should not click this option:
While we continue to work with Amazon to resolve this issue, we have temporarily disabled the Kindle book format from your OverDrive-powered website. Users will not be able to borrow, download, or place a hold on Kindle books during this time. However, Kindle books currently checked out will not be affected.
We will continue to update you when we have additional information.
We apologize for the inconvenience and thank you for your patience.
I can also add that not all websites have the warning notice displayed; mine didn't. I have also heard from one source that this bug had already been resolved, but if it hasn't then I hope this post puts your mind at ease.