I reported this before, but I'm not sure that I explained it well, and the problem still exists...
The language file 'yarpp-pt_PT.po' has a bad filename. In SVN (and so also in the ZIP), the filename has an embedded space at the end, so that it is actually 'yarpp-pt_PT.po '.
There is a bug in the PHP ssh2.sftp file wrappers such that it cannot handle filenames with spaces at the end (the space gets silently discarded as the filenames in a directory are fetched, so that it no longer matches the real filename). As a result, I can't use the automated WP plugin upgrade feature with the SSH2 login method. In fact, anyone using the SSH2 login method who attempts to upgrade the plugin will end up with the plugin being deleted.
svn mv "yet-another-related-posts-plugin/lang/yarpp-pt_PT.po " "yet-another-related-posts-plugin/lang/yarpp-pt_PT.po"