This is because ircmore was renamed to irc-more. The debian package wasn't updated but builds "successfully", because plugin pack build itself silently ignores invalid plugins (in this case "ircmore").
For a patch to add IRC More again to the package, see https://bugs.launchpad.net/ubuntu/+source/purple-plugin-pack/+bug/680820. For a patch to make plugin pack not ignore invalid plugins anymore, so that deb builds can fail and bugs like this be avoided in the future, see https://bugs.launchpad.net/ubuntu/+source/purple-plugin-pack/+bug/681680.
