OK, I requested that Remi Collett update the libssh2 & php-pecl-ssh2 packages as part of his PHP installations for RHEL/CentOS 5, and he worked on this over the weekend — updating his packages to use libssh2 1.4.3. I installed on a test system (and deactivated the ‘SSH SFTP Updater Support’ plugin…), and verified that they resolve the issue where we are seeing all the version warnings for SSH2-less-than-1.2.9 — YET I am still getting failures to delete plugins as well as the partial page error in the General -> Settings page.
I can confirm that the new libssh2 & php-pecl-ssh2 packages are working well in all other uses, so it’s not that. The libssh2 version warning was apparently unrelated. In both error cases, I am seeing at least one SFTP connect to the SSH service. (Two back-to-back connects in the case of the plugin delete action, occurring before any further HTTP requests are sent to the site.) These SFTP connects do not appear to execute any actions, according to my sftp-logging…
This behavior was definitely introduced between 4.0.1 and 4.1, and persists in the 4.2alpha.
As for “knowing the error message”, there isn’t one displayed. Nor is anything relevant logged by apache. The Settings -> General page stops silently during the page generation process, and the plugin delete operation abends after confirming the deletion (“Yes, delete these files”), but before any further request is received by the site/server. The only thing displayed in my Firefox is the browser’s generic “The connection was reset” alert.