CD4051B: MUX input structure of CD4051B

Hi Team,

My customer is using CD4051B for current sensing MUX, shown as below. it works normally when there has no high transient spikes.

But if high transient spikes appears, sometimes the CD4051 can be heated to very hot (but not damaged even after 30mins).  If power it again, it can go back to normal work (CD4051B is not damaged).

Then, we tried to add a resistor suck as 1k, CD4051B doesn't become hot anymore even transient spikes appears. 

Based on above experiments, we guess there may exist surge current to CD4051B when transient spikes appears, but we don't understand why CD4051 can be heated to very hot and not damaged. it looks like "latch-up effect“ is activated when transient spikes appears. Do you have any comments on this issue? Could you share some knowledge of MUX input structure which can help us understanding this issue and solve it?

thanks.

Best regards,

Yang