TUSB1064: SBU and AUX common voltage level change when switching

Part Number: TUSB1064

Hi

I am currently debugging some SOC design bugs which cause AUX communication error only when using with TUSB1064 together.

Now I found the SBU/AUX line common voltage is the key to reproduce the failure.

I want to understand what happens when TUSB1064 is switching and find a way to reproduce the failure without TUSB1064.

I captured the waveform when TUSB1064 is switching : 

Could you tell me why SBU1 and SBU2 ascend to about 1.6V at first?

If I can get a block diagram describing SBU - AUX switching it helps a lot!

Thanks 

Yu