Arduino DUE - slow communication rate using Wire1 with Adafruit Motor Shield V2

_From @HanaJin on February 19, 2015 20:39_

I am using the Adafruit Motor Shield V2 library to control stepper motors. Their source code uses I2C communication under the hood to control the shield. The library uses Wire on Uno and Wire1 on Due, but both have the same default I2C bus speed. An important fact is that this is THE only difference between Uno and Due as far as the 3P library source code is concerned.

However, the same command in the library is taking a lot more (hundreds or thousands times) time on Due than Uno.

I have originally posted this question to Adafruit and am recommended by Adafruit to ask here. The original post is here
https://forums.adafruit.com/viewtopic.php?f=31&t=68292&p=346159#p346159

Is there any know issue for Wire1 on Due? Thanks for any help.

_Copied from original issue: arduino/Arduino#2669_