Hey everyone,
This change to SafeCracker’s code was intentional, and it was necessary to fix a bug where SafeCracker File validation didn’t behave as expected. Pixel & Tonic will need to update Matrix to work with the changes made to SafeCracker in order for Matrix to remain compatible. There’s already an open support case concerning this at their support site, so you’ll want to follow that discussion there until P&T is able to roll-out an update.
Anything else we can help with?