This is a issue sometimes you might face when developing web apps. I am also agree the fact that this is a bad practice. But if there is a need to restrict browser's back button here is a workaround for it...!!!
http://stackoverflow.com/questions/961188/disable-browsers-back-button
cheers
Samitha.
http://stackoverflow.com/questions/961188/disable-browsers-back-button
cheers
Samitha.