empty autosaves on custom types not having support for revisions

Hi

I’ve been trying to debug this issue for hours now. The following things happen only when polylang (and no other plugins, except for e very broken down register_post_type call) is active. We have a custom type that has support for title/content, but in post_content it stores only shortcodes.

For pages that don’t have polylang active, no autosave (not auto-draft!) are fired from wordpress, hence none are created. When polylang is active though, it does activate autosave on all custom types (even when not translated) which works the first time loading the post screen. But after a few heartbeats, some script withing polylang seems to flush post_content (maybe because it contains shortcodes and they’re not executed correctly in that context) and saves it back to the *autosave*. Saving on the actual post works normally.

That has the side effect that every custom post now shows “there is a newer revision available”, because it has a difference in post_content between the post and the newest autosave/revision because post_content is empty in the autosave.

I’m pretty sure this started happening with version 2.3.6, we’ve had 2.3.4 installed previously and didn’t see that issue as far as I know.