I split a VF mount the same way.
At the track I got too much wheel hop and I felt something give. It was the bushing.
My theory on why/how they split is engine misalignment (which I'd feel confident is the OP's issue noting the off-center nature of the split). Of the few Focus's I've been under with mounts, all of them (mine included) the dogbone doesn't look straight.
In the past what I would do was install the dogbone, then the upper mounts and leave the uppers a little loose. Get in the car and load the engine to center it, rock it back and forth with the trans engaged. That seemed to help, and as a side benefit it reduced the vibration in the car considerably.
The slpit could be from a bad mold, air pockets and such. But I haven't seen hard evidence that the molds are bad yet.