Comment #1 on issue 3026 by [email protected]: staff-padding should measure to the alignment-points
http://code.google.com/p/lilypond/issues/detail?id=3026
This looks like a bigger problem...even without staff padding there is no alignment between the dynamics (at least below the staff). I'm not sure if there ever was. If there were, there'd be chain_offset_callback from DynamicText to DynamicLineSpanner at the engraving stage and a positioning-done callback for DynamicLineSpanner that uses Pango to grab baselines and align accordingly. A day-ish of work - can give guidance if needed.
