You need to look at the *whole post* in the visual editor and see if you notice anything out of whack.
Given I have no knowledge of what plugins you have running, I can only guess why it;s doing that in the first place.
These forums were CLOSED to new posts on November 19th, 2012. New forums are here: http://www.studiopress.com/forums/
and you will need to SIGN UP AGAIN.
If you need assitance with setting up your theme, go to http://my.studiopress.com/
and read the SETUP links or the TUTORIALS link on the side tab.
If you need Account Assistance
, file a help desk ticket at the same location.