My wireless internet connection broke so I went to offline mode to browse through all downloaded messages, but when clicking next message into an nntp folder started download, which in turn made the whole claws-mail hang for minutes. I find this bug critical since I also use offline mode to avoid high roaming charges and had I known that it still downloads all news, I might have saved dozens or maybe hundreds of euros. Offline mode must not use data in my opinion.
It respects offline mode.