In full blown Photoshop you do as Bobbystahr says - you can also hit Ctrl+T to just bring up the Free Transform ability to resize. You shouldn't be able to just grab a corner, drag and it resizes - it's a command function.

In elements you can grab a corner at any time and drag to resize (very annoying - this should be a command function as you could do it accidentally all the time!).

hope this helps-
-Lew ;-)