SRT and ASS subtitle format tags

[hermes14]

Hi,
I'm using smplayer 0.8.0 with mplayer rev.34578, compiled with libass support. In Options->Preferences->Subtitles I enabled SSA/ASS, but I still keep seeing those commands before the subtitle line instead of being positioned according to this spec:
{\a1} = bottom left
{\a2} = bottom middle (default placement of subtitles)
{\a3} = bottom right
{\a5} = top left
{\a6} = top middle
{\a7} = top right
{\a9} = middle left
{\a10} = middle middle
Any hint on how to actually enable them?
Thanks