I am having the same problem when I click “Save Draft”.
I thought I loose all the work I was trying to save, but if I go back to posts – drafts, the body has been saved, but the title and permalink have NOT been saved (are empty). If I try to edit the title and Save Draft, I get the same problem again.
I get another line too:
Warning: array_key_exists() expects parameter 2 to be array, null given in .../wp-content/plugins/bbpress-post-topics/index.php on line 818
Warning: Cannot modify header information - headers already sent by (output started at .../wp-content/plugins/bbpress-post-topics/index.php:818) in .../wp-includes/pluggable.php on line 876
Today I just updated WordPress (to 3.5.2) and bbPress (to 2.3.2) and bbPress Topics for Posts (to 1.7).
When I disable “bbPress Topics for Posts”, the problem goes away.
I have also posted this over at https://www.ads-software.com/support/topic/bbpress-topics-for-posts-v17-breaks-save-draft-post?replies=1#post-4374096
