No they didn't!! They went to a newer version of the compiler and made other changes that generates more efficient code, which is a good thing. A simple sketch consisting of just
arduboy.begin() in setup() is now 1192 bytes shorter (9274 bytes instead of 10466 bytes)!
We borked the Arduino library by writing a function using open loop code that creates a timing delay by adding extra instructions that do nothing. The more efficient compiled code caused the overall delay to be too short, causing the function to write to the display too fast.
The blame for the display corruption problem that results from upgrading to Arduino IDE 1.6.10 is all on the Arduboy library!
My fix changes the function to a closed loop. Instead of a blind delay, it waits for the SPI controller to tell us that it's ready to accept another character. With this change, the problem will never occur again in the future and is also fully backwards compatible with all older IDE versions.