Negative Voltage on the Vin of the XTR111

Hi,

I'm using an XTR111 as a voltage to current converter; but my signal input can be both positive and sometimes negative.
So i put a 1N4148 diode to protect my input but when input voltage went beyond -700mV, my XTR111 current output is about 34mA and the potential difference between mys Rset (3,6kOhm) is about 11,8V.

I would like to know why i get a current output of 33mA when my input voltage goes beyond - 650mV

Thanks for your answers

Jonathan Drack