I knew there was a limit, but I didn't take the time to test it before today.
According to my tests, the limit is 65 534 characters per Print statement. When the string you're printing is above this, something strange happens.
I made an agent with a For .. To loop to concatenate a string. The string contains the counter and a line-break per loop.
String length: 65 193
Last line printed: 5100 (Correct, For 1 To 5100)
String length: 70 393:
Last line printed: 414 (Wrong)
String length: 78 193
Last line printed: 1059 (Wrong)