it has not done this since i repaired my tables, and removed the rogue "custom" entry created the other day while trying to coax "posts in context" to show up as a group block.    i later learned that after you have adjusted settings, all older posts will not show up in the group timeline, only newer ones.  i had not installed timeline because i didnt want to confuse most users between "posts and update" because most people do not understand the difference.
in addition, what would be fantastic is if when a user posted a link inside a post or an update, as with the "add" link button that triggers the iFramely script, to be triggered when a link is pasted in plain text as well, and turns blue inside the tinyMCE.
this is a design issue, which becomes a usability issue.   because people paste youtube links and dont understand why they are not making an embedded iFrame.   ("but its not pretty like your links are!"), id rather an extra layer that scans tinyMCE entry for links and triggers the iFrame generation ON SUBMIT, but not "live". if that makes sense..