Inserting new line on edit

Alright, this is weird and after searching I still can't believe no one else has had this problem before, so maybe I just have something configured stupidly. I have tried disabling a number of other modules, but haven't noticed that any of them change this behavior.

The first time I create a node and insert the <!--break--> everything works as expected. The teaser ends where it should (I am usually placing this mid-sentence) and the body is fluid with no indication of where the teaser break occurs. In mysql the body is saved as this:
has fallen and<!--break--> Anseana

If I then edit the node, the teaser will be separated into the summary editing window and the body in the lower window. If I save it while it is split in this way, regardless of whether i edit in either window, it is saved with a new line after the teaser section and then again after the <!--break-->. This is written to the body in mysql:
has fallen and
<!--break-->
Anseana
If the Line break converter is turned on, and I have formatted the site for it to be turned on, this results in a very undesirable break in the flow of the body.

I have been working around this by clicking Join Summary, putting the <!--break--> back in (it's just gone after you click join summary) and deleting the two new lines. This has gotten old, though, so I thought I'd bring it up and see if anyone has any suggestions.