Re: Denial is the first defence.
Although, when I worked at Xerox, I designed and built a laser printer driver for a new product. The developers claimed I was sending a bogus character so I put in microcode a logger that logged every character sent and received. Nope, no extra characters.
So I went to the developers lab using my hardware and software and they had put a terminal in parallel with the laser printer. Sure enough, there was an extra character. After some head scratching i noticed that the character was sent when the software terminated. A few minutes later I discovered that resetting the UART was causing the extra character to be sent (after my microcoded logger had shut down). Easy fix was to output a MARK before resetting the UART.
Sometimes the customer is right and it pays to keep an open mind.