[This tip is also great if you use a mouse to copy and paste command lines in your window.]
Some terminals I've used (like old Hewlett-Packard and Tektronix terminals) had local editing. You could move your cursor up the screen to a previous command line, maybe make some edits to it, then press a SEND LINE key to resend that line to the host. This didn't have anything to do withlike some UNIX shells have now. Maybe your terminal can do that, too.
The problem was that unless I erased the shell prompt (
set prompt=' '
That's right: four spaces. Most UNIX commands start their output at column 1, so my command lines were easy to find because they were indented. And the shell didn't care if I sent four spaces before the command line. So everything was fine until I got my new terminal without a SEND LINE key...
(If you want some information in your prompt, too, make awith four spaces in the last line.)