percussion clef

[Nick Didkovsky]

Hello

At some point in LilyPond's history I believe the notes on the staff 
with a percussion clef showed up on the same level as treble clef.
In other words...
\clef percussion
c''4
...and...
\clef treble
c''4
...both resulted in a C displayed on the second space from the top.

Today I revisited some scores and discovered that he notes on the 
percussion clef are moved up a number of levels.
To fix it I now add a change to middle c position, ie:
\clef percussion
\set Staff.middleCPosition = #-6
c''4

Does anyone know when (ie what LilyPond version) and why this changed?  
Confused...

Thanks
Nick Didkovsky