Cannot save post edits if revision limit has been reached

I just had the strangest of issues: I could not save changes to existing posts if the maximum number of post revisions had been reached. Of course WordPress is supposed to delete the oldest revision in such a case but that did not happen. Instead after clicking “update” everything went as always, but when the page refreshed the changed content was gone.

I tried this on two different posts where the maximum revision number had been reached. Saving worked correctly on a third post where the maximum revision number had not been reached yet.

Through this post I found that I could add individual characters to the posts that would not take changes.

I tried disabling W3 Total Cache and restarting Apache to no avail. Finally restarting MySQL fixed the issue.