If "Copy & Past" is used a lot, this causes the phone (Galaxy S3) to reboot when the clipboard reaches a certain amount,
Solution or workaround:
"Launch the text message app.
Tap New Message
Press and hold the "enter message" area for few seconds
It will pop up clipboard
tap clipboard
You will see what is stored on your clipboard. Tap and Hold the clipboard items for seconds,
You will have a option to delete from clipboard or tap clear to delete all the clipboard contents "
Samsung seems to be aware of the problem, but have not released a fix.