If you encounter this behavior when editing the code from the Details layout tab in the Manage Directories section, please double check the PHP Settings of your server(System information > PHP Information), since this is caused by a server configuration, not the RSForm!Pro component. More specifically the extra signs are generated by the Magic Quotes settings.
This can be easily resolved by creating a php.ini file in the root folder of your installation and adding the following line in it:
magic_quotes_gpc = Off
If this does not resolve the issue you will need to contact your hosting provider regarding this matter and ask them to disable the Magic Quotes from your server's main php.ini file.