I also consider this to be a bug. The original Pine handled these HTML attachments (which are a nuisance, I think we can all agree) significantly better and allowed viewing them from within the program itself, not requiring x11 forwarding.
Many senders nowadays only include the relevant part of the email as HTML (with the "ASCII" part only containing a few lines of useless text), and the option to have it rendered internally by alpine (or even call lynx/elinks2 as a quick text-render workaround) would be *highly* appreciated. -M