CC65: Four lines bad, two lines good?

Question

I'm trying to do IO using stdio.h on a Commodore 64, but I'm having with even the following program:

#include <stdio.h>

void main(void)
{
    printf("Foo\n");
    printf("Bar\n");
    /* printf("Foo\n"); */
    /* printf("Bar\n"); */
}

The problem is, if I leave 2 printfs uncommented, then it works as expected. If I uncomment all four, then it doesn't work at all: if I RUN it, I just see the lines flashing by before the screen resets to just showing READY. on an empty screen.

If I have three, then it doesn't work for the first time (flashes to empty READY. screen) but if I RUN it again, then it works...

I should add that I've only tested this on VICE, not a real C64.

Answer 1

After following @Devolus's suggestion to do sanity checking with sleep, it turned out nothing, in general, was working properly. I've downgraded my CC65 installation from 2.13.9-svn5804 to 2.13.3, and that seems to have solved my problem.