Some terminal emultors (xterm for example) do not rewrap already printed text if the window is resized. Instead everything outside of the new window is just cut off. This text is then lost and not just hidden.
+--------------+ +-------+ +--------------+
|$ hello | |$ hello| |$ hello |
|Hello World! | |Hello W| |Hello W |
|$ | -> |$ | -> |$ |
+--------------+ +-------+ +--------------+
If you want to retain the text you will have to use another terminal emulator. ROXTerm for example really just hides the text and you can read it once more after the window has again the original size (I'm not sure if there is a way to scroll horizontally while the window is smaller). rxvt-unicode wraps each line that is to long, so that you can read everything even after a resize.
ROXTerm:
+--------------+ +-------+ +--------------+
|$ hello | |$ hello| |$ hello |
|Hello World! | |Hello W| |Hello World! |
|$ | -> |$ | -> |$ |
+--------------+ +-------+ +--------------+
rxvt-unicode:
+--------------+ +-------+ +--------------+
|$ hello | |Hello W| |$ hello |
|Hello World! | |orld! | |Hello World! |
|$ | -> |$ | -> |$ |
+--------------+ +-------+ +--------------+
See here on how to change the default terminal emulator
What terminal emulator are you using? How is the first terminal being "hidden"? What layout are you using with the two terminals (tabbed,tiled etc)?