for example this line.
while (!usbInterruptIsReady()) usbPoll(); usbSetInterrupt( reportBuffer, ;
will not fire in my driver if a control transfer occurs at the same time. I can see the normal 8 ms apart from my polls are extended to 16 ms for the collision. So the driver had to hold off for 8 ms. I would have assumed the bulk transfer takes priory but it does not.