ctrl+c closes terminal window completely - why / how?

I have a process, and when I issue ctrl+c in the terminal, it closes the terminal window completely, anybody know why that might be happening? This is how the process is now started: exec "$(dirname "$0")/suman-shell" # a it used to be started like so, and there was no problem: "./$(dirname "$0")/suman-shell" # b it does look like using exec is what is causing the terminal window to close, so why does a close the terminal window, but not b, after receiving a signal?