I would agree with Andy that it must be lcd_write() if writing to the serial port is ok.

With the code fragment you've posted I really don't know, but consider the possibility that your hard coded text ("HI") is certainly stored in code memory while the result of the "%d" is going to be stored in some kind of RAM, either internal or XRAM.

I've never messed with using custom putchar/printf functions, but I wouldn't be surprised if the problem has something to do with the fact that there are different types of memory involved. That which comes from code memory seems to be working while that coming from internal RAM/XRAM seems to be having some problems.

Just a thought for a possible line of investigation.

Regards,
Craig Steiner