First, and most important: DOSBox emulates MS-DOS 5/6, so it does not support the /P parameter on the SET command.

If you are using an SVN build then you will get an error exit (not a "crash") when you try to use a /P parameter with the SET command, and in the console window you will see this message: "Set /P is not supported. Use Choice!", so please take that advice and use the CHOICE command instead.