There is a distinction between the return key and the enter key keys. In some multiple-mode terminals, that can switch between modes, pressing the key when "not" in block mode does not do the same thing as pressing the key. Whilst the key will cause an input line to be sent to the host in line-at-a-time mode, the key will rather cause the terminal to transmit the contents of the character row where the cursor is currently positioned to the host, host-issued prompts and all.