@bellan  @vadler  @bachtis

This "bug fix" was introduced in 535.
It introduces data content inconsistency for all previously created muons.
So, people can't rely on this quantity at all, unless everyone is consistently reprocessing muons.
A more consistent fix was added on the data member access side in
http://cmssw.cvs.cern.ch/cgi-bin/cmssw.cgi/CMSSW/DataFormats/MuonReco/interface/Muon.h?r1=1.71&r2=1.71.2.1
The original "bug fix" in the MuonIdProducer was then removed and release 535 was killed.

Nothing has changed since then, in fact the situation is even more "final".
So, I prefer to stick to that old choice.
If we want to rely on this fixed value, we have to recommend to rerun all high level muon reco chain, which is not feasible.