[mitosis]

Those of us old enough to remember the early days of the Macintosh know that this is nothing new. Apple programs used undocumented calls to QuickDraw and did all kinds of yucky stuff with the upper 8 bits of the address (in the early days, the Mac processor used 24-bit addresses but the registers were 32-bit), which lead to the "32-bit clean" problems that plagued the first Macs to use 32-bit addressing.

Apple also did this in the Apple II days, calling undocumented ROM monitor routines from their own programs and operating systems. In fact, several companies made a list of those entry points and considered them "semi-official", the reasoning being that Apple wouldn't change entry points used by their own programs.