Canon released new firmware version 1.0.3.1.00 for the C100 Mark II:
http://texasmediasystems.com/canon-c100-mkii-firmware-update/

Fixes the phenomenon in which the aperture adjustment may not operate as expected when using the control dial on the grip unit when certain EF lenses* are attached. This occurs with EOS C100 Mark II cameras running Firmware Version 1.0.2.1.00
http://texasmediasystems.com/canon-c100-mkii-firmware-update/
