I got a reply from Mike Bombich about the issue I raised in the "How to Rate Yosemite?" thread. First, I sent him this report:

I have copied the fonts (System/Library/Fonts; ~/Library/Fonts) from my new installation of Yosemite to an internal drive with no operating system on it (Data B1). When making a clone of Data B1 to Data B2, CCC 3.5.7 reports media errors as shown in the attached file. It only affects .ttc fonts from the Yosemite install. There are plenty of .ttc fonts from previous OS installs that copy perfectly. If I delete the suspect .ttc fonts and start the same clone, CCC reports no bad blocks and copies perfectly.

BTW, FontDoctor crashes every time I try to diagnose one of the Yosemite .ttc fonts.

Then added this:

Further to my error report: I only have the bad blocks/.ttc fonts problems when I make a clone while booted into 10.6.8 using CCC 3.5.7. If I am booted into 10.10 and using CCC 4.0, then the clone of the fonts folder works perfectly.

If, while booted in 10.6.8, I copy a Mavericks .ttc file to the desktop, it copies normally. If, however, I try to copy any .ttc file from the Yosemite install, I get an IO error –8084.

I wonder if there is some sort of protection on the new Apple fonts? It seems to be an Apple problem rather than a CCC problem?

This is his reply:

Apple introduced some changes to HFS+ filesystem compression in Yosemite that are not backwards compatible. If you want to access any system files on a Yosemite volume, it must be done on a system running 10.9.5 or later. CCC 4 will warn you if you attempt to copy a 10.10 volume while booted from an OS older than 10.9.5, but CCC 3.5.7 was released before that information was available, so it can't give you the right advice on that scenario.

I hope this helps. I know I am finally going to have to bite the bullet, abandon Adobe GoLive, and start another learning curve. This four-year-old Mac Pro will last a few more years, I hope, then I see a Retina iMac in my future. No Snow Leopard then...

Good information freelance, thanks to you and Mike Bombich for passing it along. This probably explains the inability some have encountered of Yosemite to see volumes with prior OS versions installed.

It is really bad news for users who might want to go back from Yosemite to previous OS versions or users attempting to use a dual boot with Yosemite and a previous OS X release.

There is a way you can do this: you can install Snow Leopard Server (which you can still download if you're a registered Apple developer) under Parallels. The 'regular' version of Snow Leopard won't run in Parallels (for licensing, not technical, reasons).

I too bitterly resented giving up GoLive, and for a while I ran it on Snow Leopard in Parallels. I've finally, grudgingly, moved to Dreamweaver, but it simply isn't as good.