Hi Chet,
using readline-7.0-testing with ipython 4.1.2 and the TkAgg (or GTK3Agg) backend for matplotlib, I observed the following behavior:
1) open ipython in pylab mode (ipython --pylab or use the %pylab magic once inside the repl).
2) Type something.
3) Press Ctrl-C: line edition is not aborted as expected.
It seems it has something to do with an interaction between SIGINT handlers and matplotlib backends. Maybe the bug is in ipython but I'm not able to conclude that by myself. One thing I can tell is that it doesn't happen with the Qt5Agg backend.
Cheers
--
Carlos