Helvetica is a great typeface. And although any respectable designer has an appropriate regard for Helvetica, it seems that Apple is a bit love drunk over the whole thing.
Have you notice how many versions of Helvetica you have on your Mac? Helvetica LT MM, Helvetica.dfont, HelvecticaCY.dfont, HelveticaNeue.dfont, maybe more.
It’s like a secret alliance hiding in the depths of your font folders. Gives me the creeps.
and of course having all those Helveticas hanging around makes problems.
Apparently the only solution is to buy and install an OpenType version of Helvetica with a slightly different name and only and forever use that one. Just ignore the others.
Or you can use a font manager to manage your system fonts.