I went into a subfolder of an archive I had, extracted some large files and then deleted those files from the archive (but did not save it). I then extracted the parent folder and watched the progress bar move along but it did not finish once it reached the end. It was a while later when it actually finished, as if was also extracting the files I had deleted (though they did not appear in the result). I'm guessing it could be difficult to extract the files minus the deleted ones before saving but do you think it would be possible?
[edit] I guess there are all sorts of complications when extracting from an unsaved archive. This is just one I encountered.

A minor problem: Cannot extract an empty folder from an archive from within BetterZip (it does work with Extract All or when extracting the empty folder's parent). Probably a very rare occurrence, I only discovered this while testing another problem which I can't seem to reproduce anymore.