K8064 lack of smooth light on/off transition

I am running a K8064 dimmer controlled with a 12bit DAC (@5VDC), raising and lowering the control voltage about 1/10th of a volt per second. At several locations in the transition from 0 to 5V, or reverse, the driven 110V 20 W Xeron light(s) show a visible bump in brightness. Everything is working fine except for the transition bump. The 12bit DAC is certainly delivering stable and smooth DC voltage.

I should point out that I have a similar circuit driving the now obsolete K8003 without this problem.

Any suggestions, or is this just an inherent snag in the K8064 operation.

Fred Miller