This thread has been worrying me, so I did a little test myself. I give it to you for what it's worth. This said, I hope Corel people don't mind us doing their job, so they can sit back as they did on my support call?
I have a 15" MacBookPro, begin 2011, intel i7 at 2,2GHz, 8GB internal memory, video card Intel HD Video 3000 512MB. running MacOSX 10.7.5 and Toast 11.1 (1072) Titanium, with plug-in for Blu-ray burning onto DVD's. My disk burner is Pioneer BDR208, mounted in LaCie d2 drive (updated the firmware from LaCie site). The disks are Panasonic LM-BRS2MWE25, special archive disks (25y). I burn Data, Mac & PC, archiving video footage, nearly always spanned.
So far, Toast has done a good job for me (after I found out about the firmware update). It's much too slow, but that's another thread, see elsewhere in this forum. I installed Mac OSX 10.8 on a stick, started up, installed Toast under the new OS and tried to burn a small project spanned over 3 CD's. It worked fine. I have good hopes, that Toast will continue to do its job, but perhaps any of you has a suggestion for further testing? Would things go different using spanned Blu-rays (I would hate to see them go waisted).
My only concern right now is, that the whole program will be off the market soon, given all the bad experiences. It took me long to buy the license (because of initial bad experience re full price for upgrading, I had to swallow longtime), but I really see no alternative program, offering the same functionality. They are on top and they know it, so they think they can afford to be arrogant and for the moment they're right.