1) A plugin is already existing and was installed by using the download url http://example.com/foo.tgz
2) The plugin get's updated/re-installed by using download url http://example.com/bar.tgz
3) A dir rename is needed because the archive behind URL http://example.com/bar.tgz
is creating a dirname != the module basename in the first step (like is the case for all the zipball/master github links).
4) The rename will not happen, therefore there are two plugin dirs using the same resources. The wiki dies with a PHP error at inc/init.php because the classes can't be redeclared. This will only happen if a rename is needed. If the archive behind http://example.com/bar.tgz
directly creates the needed directory name, everything is fine.
I discovered this after creating a new release of the MetaHeaders plugin. However, I think other users are also affected, cf. "http://forum.dokuwiki.org/thread/8106" where a "MrBertie-pagequery-4d2eb03" directory was created.
====== How to reproduce ======
1. Install an old MetaHeaders release from "http://cloud.github.com/downloads/chimeric/dokuwiki-plugin-metaheaders/plugin-metaheaders.tgz" by using the plugin manager. Go to "/lib/plugins/" to list the existing folders. You will see "metaheaders" there.
2. Update the metaheaders plugin to the DEVEL version by using "https://github.com/andreashaerter/dokuwiki-plugin-metaheaders/zipball/master" as download URL. As you can see, the new plugin folder "andreashaerter-dokuwiki-plugin-metaheaders-080f7be" was created but not renamed to its basename "metaheaders". The wiki is dead now because the "metaheaders" dir from "1." is also existing.
3. Delete the "lib/plugins/andreashaerter-dokuwiki-plugin-metaheaders-080f7be" to bring the wiki back to life. Update the metaheaders plugin to the current RELEASE by using "http://andreas-haerter.com/downloads/dokuwiki-plugin-metaheaders/latest" as download URL. This points to an archive which directly creates the needed "metaheaders" dir so no rename is needed because it was made by using a proper archive prefix:
git archive --format=tar --prefix=metaheaders/ HEAD | gzip > ~/$(date +"%Y-%m-%d")_metaheaders.tar.gz.
Everything works as expected then (beside FS#2463