Valgrind reports the following error:
==8649== Invalid read of size 4
==8649==    at 0x4BA0ED9: r300EmitArrays (r300_maos.c:172)
==8649==    by 0x4B9648A: r300_run_vb_render (r300_render.c:341)
==8649==    by 0x4B96E8E: r300_run_tcl_render (r300_render.c:540)
==8649==    by 0x4C128A0: _tnl_run_pipeline (t_pipeline.c:159)
==8649==    by 0x4C9E8D8: _tnl_draw_prims (t_draw.c:400)
==8649==    by 0x4C97F42: vbo_exec_vtx_flush (vbo_exec_draw.c:215)
==8649==    by 0x4C93885: vbo_exec_wrap_buffers (vbo_exec_api.c:75)
==8649==    by 0x4C93D85: vbo_exec_vtx_wrap (vbo_exec_api.c:109)
==8649==    by 0x4C97289: vbo_Vertex3fv (vbo_attrib_tmp.h:61)
==8649==    by 0x4837BE1: glVertex3fv (glapitemp.h:770)
==8649==    by 0x42C32CE: osgParticle::Particle::render(osg::Vec3f const&, osg::Vec3f const&, osg::Vec3f const&, float) const (in /usr/lib/libosgParticle.so)
==8649==    by 0x42C9633: osgParticle::ParticleSystem::single_pass_render(osg::State&, osg::Matrixd const&) const (in /usr/lib/libosgParticle.so)
==8649==  Address 0x4DADB00 is 0 bytes after a block of size 65,536 alloc'd
==8649==    at 0x40227F4: memalign (vg_replace_malloc.c:448)
==8649==    by 0x4022844: posix_memalign (vg_replace_malloc.c:549)
==8649==    by 0x4BD5269: _mesa_align_malloc (imports.c:113)
==8649==    by 0x4C94329: vbo_exec_vtx_init (vbo_exec_api.c:638)
==8649==    by 0x4C935DC: vbo_exec_init (vbo_exec.c:52)
==8649==    by 0x4C934D0: _vbo_CreateContext (vbo_context.c:223)
==8649==    by 0x4B8CAA5: r300CreateContext (r300_context.c:297)
==8649==    by 0x4B84D9C: radeonCreateContext (radeon_screen.c:920)
==8649==    by 0x4B815A9: driCreateNewContext (dri_util.c:830)
==8649==    by 0x480A64E: CreateContext (glxcmds.c:353)
==8649==    by 0x480A984: glXCreateContext (glxcmds.c:430)
==8649==    by 0x48924DD: Producer::RenderSurface::_init() (in /usr/lib/libProducer.so)

It seems that somehow in emit_vec16 in r300_maos, data has less allocated memory from what count thinks, by one,
so we read out of the data bounds.

for (i = 0; i < count; i++) {
        out[0] = *(int *)data;  // Valgrind warns here
        out[1] = *(int *)(data + 4);// Valgrind warns and here
        out[2] = *(int *)(data + 8);// Valgrind warns and here
        out[3] = *(int *)(data + 12);// Valgrind warns and here
        out += 4;
        data += stride;
}

This happens when using a simple model which is not rendered correctly in blender and OSG.
The black line should not exist. Toggling light seems to remove the black line.