The BibTeX format offers a "proceedings" type, which is the collection of all articles from a specific conference. However, when I import a bibtex entry starting with @Proceedings, refbase identifies it as a "Conference Article" (@InProceedings).
I've tried to export entries into RIS format, which, I guess, is used internally by refbase, and both entries (@Proceedings and @InProceedings) have the same type - CONF.
Is there any way to solve this problem?
Your assessment is correct: refbase converts to RIS, which does not have a separate type for conference volumes. I believe the only solution would be to have a separate native PHP import facility for a format that supported a separate proceedings type. I had thought that someone who couldn't use bibutils on their server had been developing native BibTeX support, but I don't know what happened with this effort.