On turn 1 of Silvertone (North), you only have to go partly onto the outside kerb coming out of the corner and you lap gets DQ'd, you don't even get a time penalty. On the full GP circuit the cut detection here works as you would expect and you can run onto the curb without any problem. Even if you follow the green suggested driving on the northern circuit you end up with a DQ.
This fault has been with us since the track was released and is due for a fix. Below is two shots which show how little you have to go onto the curbs to get a DQ.