I have been working on this chip for a few days and have been running into the same issue. I have 3 chips and all three exhibit this behavior. On the scope you can see that the chip is responding to the bus but it is unable to drive the signal low. On the scope it for whatever reason pulls the signal to 2.5v and I have been unable to figure out why. I know it isn't a problem with the bus itself because i have plenty of other chips working just fine on the same line.