buttons do not appear with a cache clear

The site has 'cache pages for anonymous users' on and block cache off. It uses Drupal's default Mysql cache backends. The buttons added by this module regularly disappear from the content pages. Clearing caches brings them back. There are no logged errors.

When a new users signs up, Rules creates a page for that user, which that user can edit when he becomes authorised (using Login Toboggan, where authorisation means removing the role 'pre-authorized'). The role 'pre-authorized' has permission to use Save & Edit. Once the buttons have vanished for one user, they have vanished for all users, so it does not look like a permissions issue.

I cannot yet reliably reproduce the bug although it has returned many times. Maybe there is a workaround (for example disabling caching of the node edit form?).

The site is on Apache, php 5.5 (including Zend optimiser +).