pending revision block disappears after editing.

This is a strange one.

The other day I noticed that the pending revision block disappeared. I couldn't figure out why. I went back to a dev version of the site used recently for other issues I was having with Revisioning and the block was there. I set all the modules and permissions on both sites to those on dev. I couldn't get the block to reappear on the live site and I couldn't reproduce the problem on the dev site.

Then when I viewed the blocks configuration, and saved it on the dev site, it disappeared. After resetting both sites and again and editing the block, it disappeared on both sites even though no changes were made to the configuration. There doesn't seem to be any configuration of the block which doesn't result in a missing block.

Also, I noticed that when on the page of a node that has pending revisions, clicking on the revision tab has a different behaviour before/after editing the block. Before, I am taken to the View subtab (/node//revisions//view) which I think is the expected behaviour. After, I am taken to /node//revisions (the list of revisions).

I can provide access to the dev site if someone wants to see the behaviour for themselves.

Any help is appreciated.