Reading the initial post and without looking at the response I was about to say - plug-ins.
I think OSX has made plugin makers a little slack in their writing.
I remember OS9 had more stable plugs......or maybe it was because there were less of them under less varieties.
Then again the plugins were one of the only stable things in OS9. lol.
Can updates effect the way older plugs work?
Could a plugin working under 10.2 and metro 6.05 suddenly have trouble in 10.2.8 and metro 6.1?
sigmasix - more info needed.
especially if you're not working with effects.
any 3rd party device plugged in like a midi interface?
scoot.