Teaserbreak won't undo

I added a

with the editor but am now unable to undo it!

If I edit the node the

has disappeared but drupal has split the teaser in a seperate part as if I had clicked on "Split Summary at Cursor" button.

I can join using that button but even if joined the teaser will break at the point I added

in the first place.

If I set a new break with "Split Summary at Cursor" button it will break there but as soon as I tell him to join (which seems to undo this button use correctly) it again splits at the point where I placed the

in the beginning.

How to get rid of this break so he won`t break at all?