Thank you very much, tshering!
I will stay on 07 for now until the stable 08 release will be available. I have no issues and I can wait some time. After all, I use the calibre only for conversion and I won't allow it to communicate with my devices. I'm only sideloading my books directly on them (the only reason is that I want to create categories folders based on authors and place the epubs inside them. It is more easy that way when I'm browsing with Koreader's file manager).
I'll keep following the current thread for more infos.