vimpulse bug: C-f (viper-scroll-screen) doesn't work in visual mode

Dear vimpulse developers, in visual mode, I'd expect C-f (viper-scroll-screen) to extend the visual selection. However, it doesn't do anything, it feels like being stuck. Workaround: use <next> (scroll-up). Cheers, Christoph -- Christoph Lange, Jacobs Univ. Bremen, http://kwarc.info/clange, Skype duke4701