printf messages show up after about 10 of them are sent

Question

I have a short code like this:

main() {
    while(1) {
        printf( "TEST1 " );
        for (int pos = SERVO_OPEN_POSITION; pos < SERVO_CLOSED_POSITION; pos += 25) {
            Manipulator.SetPosition(pos);  
            wait_ms(20);
        }
        for (int pos = SERVO_CLOSED_POSITION; pos > SERVO_OPEN_POSITION; pos -= 25) {
            Manipulator.SetPosition(pos); 
            wait_ms(20); 
        } 
    } 
}

I have a servo that I'm just spinning inifnietelyin both directions. After each cycle of servo doing its work I printf a message "Test1". So, I'd expect to see "Test1" in terminal (Tera Term) each time a servo starts a new cycle. Instead, I see nothing until about 10 cycles are done. Then on the terminal something like this shows up:

TEST1 TEST1 TEST1 TEST1 TEST1 TEST1 TEST1 TEST1 TEST1 TE

So I get about 10 messages at once (and often last of them is cut (TE)). After that, again, I have to wait about 10 cycles for next batch of "TEST1" messages to appear.

I also tried doing very similar thing, but without a servo - I just removed

Manipulator.SetPosition(pos); 

from the program. Result was the same.

Why is that?