Well to be sure of that, you need to prove that you are actually sending CR+LF over the serial line 
Did you set it in gtkterm? If so you might want to doublecheck the tty settings as they may (partly) reverse the effect of the CR-LF sent by gtkterm (like if you see icrnl, igncr, inlcr and the like).
As every symptom you see looks the same as the issue I had it reminds me of the saying "if it looks like a duck, walks like a duck and quacks like a duck, then it's probably a duck" (but "probably" isn't good enough either, I know).