MacBook Pro SMC Firmware Update 1.5
Apple has released MacBook Pro SMC Firmware Update 1.5 for unspecified models of the MacBook Pro, running either Mac OS X 10.7.2 Lion or 10.6.8 Snow Leopard. The update reportedly fixes a bug that could cause the MacBook Pro on a power adapter to shut down unexpectedly under heavy load if the battery charge level (which you wouldn’t think would be at issue) is near empty. To install this update, your MacBook Pro must be plugged into power or be at least 25 percent charged; as with all firmware updates, do not interrupt the update while it’s installing. Because Apple isn’t saying exactly which models of the MacBook Pro are affected, we recommend getting this update via Software
Update. Presumably, the updater itself also knows not to install itself unnecessarily. (Free, 730 KB)
If I had to make a guess, it's partially in reference to http://www.topclassactions.com/lawsuit-settlements/lawsuit-news/1382-apple-macbook-pro-defective-battery-class-action-lawsuit- where it has been observer (and I've seen this on my Early-2011 MBP) that under heavy load the charger is insufficient to keep up and the system drains the battery to make up the difference. It sounds like the patch doesn't completely fix the problem though...that would take a power supply that can output more than 85 W.