It appears that the Seeed motor shield conflicts with the standard ethernet shield by using pin 10 to control bridge B. When using the motor shield with the standard ethernet shield, the SPI bus pins must be shared between three different devices: the motor controller, the ethernet controller, and the sd card controller. The ethernet shield uses pins 4 and 10 to reserve usage of the SPI bus by the sd card controller and ethernet controller, respectively.
Unfortunately, the Seeed motor shield also uses pin 10 to enable controller bridge B, which uses the same SPI pins. This makes it impossible to use the motor shield bridge B along with the ethernet shield’s built-in SD card. One must be disabled. While it is easy to disable the SD card controller using its (unique) pin 4, it is impossible to disable bridge B using pin 10, because doing so enables the ethernet controller on the same pin.
Can I use the SenseB jumper to disable bridge B?
Would you consider switching to a different pin, that does not conflict with other SPI-dependent shields, to control bridge B in future versions?