not sure if this is really a bittorrent sync problem but when syncing audiobooks in m4b format to my iphone (4, 5.1.1) i can't open them in any application. they aren't offered in the open with list, it offers stuff like teamviewer and dropbox, even ifile but ifile can't open the files with it's audioplayer either. same files synced through itunes open fine. ideas?