I just started having this same problem last night as well. It seems to be a series of printfs that are in a single if block. I can comment out any combination of them and get the same result. The one thing I didn't check was passing a byte as an argument although Ithink I've done this in the past without problems.
Subsequent printfs don't seem to be a problem. One symptom is that I have multiple lines in single printfs (ie. printf("x=%d\n\ry=%d\n\r", x, y)
I get the first character of each line not just the first character of the printf.