Flipping flags in internal code is an incredibly easy and common error to make. There are some estimates suggesting that it is actually more common than off-by-one errors - but not as often caught because it is much harder to see the error. (According to legend I heard the very first Fortran compiler made this error - the flag determining whether to compile carefully or not was reversed. No idea whether that is true.)

As far as I am concerned the entire question of whether summon/get is OK is much less important than getting flags reversed. As matters stand, I don't think people would accidentally call summon, and most of the time get is right. But flipping flags is a basic error that you will make again and again...