Hi Michal,
Let me provide you a workaround, check with that.
As I see that you are deleting the ebooks from the c:\Users\Admin\Documents\My Digital Editions, but ADE is still remembering that you have the ebook on your computer.
In this case, I assume that, there is a different file which keeps all the records for the ebooks, i.e. Manifest.xml file.
So, if you are able to re- download all the ebooks from library, please go ahead and delete the Manifest file from c:\Users\Admin\Documents\My Digital Editions.
Check if this works for you.
Regards,
Yuvraj.