Unable to send SIGINT (C-c C-c) to a process running in ansi-term

Question

In Emacs, sometimes I start a shell with ansi-term, and then from this shell I run IPython (another shell) that enters a long loop printing a long, long output.

When this happens, I often want to sendSIGINT to stop the script that IPython is running, but sometimes this takes way too long for IPython to capture Ctrl+C Ctrl+C (there are times when IPython never seems to listen to it). Interestingly, this does not seem to happen when I run it from a regular terminal.

Why is this the case? Is it an Emacs or IPython problem?