When positioned at the end of an outline node, blocks will spill their
background color (defined by the `org-block-end-line' face) when the
node is folded.

To see this, paste the following lines into an Org buffer, and make
sure that a background color is set for `org-block-end-line':


* One
#+BEGIN_SRC
#+END_SRC
This is OK, it won't spill.
* Two
This will spill.
#+BEGIN_SRC
#+END_SRC
* Three
Spill is gone now.


When the node "Two" is folded, the background color will still be
painted all the way to the right fringe (as can be viewed here:
http://folk.uio.no/simenheg/org-spill.png). This becomes especially
prominent when using a theme that sets a background color for
`org-block-end-line', for instance the built-in Leuven theme.

Emacs  : GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5)
 of 2015-03-07 on trouble, modified by Debian
Package: Org-mode version 8.3beta (release_8.3beta-1145-g45555d @ 
/home/simen/src/org-mode/lisp/)