4.3.1 ‘Auto wrap mode initially on’
Auto wrap mode controls what happens when text printed in a PuTTY window reaches the right-hand edge of the window.
With auto wrap mode on, if a long line of text reaches the right-hand edge, it will wrap over on to the next line so you can still see all the text. With auto wrap mode off, the cursor will stay at the right-hand edge of the screen, and all the characters in the line will be printed on top of each other.
If you are running a full-screen application and you occasionally find the screen scrolling up when it looks as if it shouldn't, you could try turning this option off.
Auto wrap mode can be turned on and off by control sequences sent by the server. This configuration option controls the default state, which will be restored when you reset the terminal (see section 3.1.3.6). However, if you modify this option in mid-session using ‘Change Settings’, it will take effect immediately.