Lpc2000

I have a problem where the MCU won't boot up. I discovered that if I have no power on my 
board but with a serial cable plugged in, the serial driver drives VCC to -0.5V (max), 
probable leak since RS-232 Rx input is negative voltage. When I power up my board, the 
chip won't boot up. But if I kill power to my board but reapply power again before VCC 
drops below 0V, the chip would boot fine (this is possible by the way because of some 
large caps on my board, so VCC doesn't immediately go down to 0V).

Now my question, should the MCU boot up when you power up from negative VCC as little 
as -0.5V? Should a reset chip (I'm using TPS3836 3.3) help? In my case, it doesn't. Thanks.

-John G-