Speed is not controllable on Bank A Motor 1 when using Arduino IDEs that have an I2C frequency other than 50000. Mindsensors support is currently working on a fix for this issue.
This turned out to be a problem with the hardware. Pre-production boards from our kickstarter campaign will have this issue but it has since been fixed and later models will not have this issue.
Speed is not controllable on Bank A Motor 1 when using Arduino IDEs that have an I2C frequency other than 50000. Mindsensors support is currently working on a fix for this issue.