I believe I've just discovered a bug. Running the development version of lily (2.17.5, commit bc4b56a8dee39a1fa3f40ac329ab0754d46fc56f )
the following snippet produces two notes next to each other, without any visible barline at all. See the attached image.
I checked it in the current documentation and it seems that the dashed barline ought to work as it did in 2.15. ( http://lilypond.org/doc/v2.16/Documentation/notation/bars#bar-lines )