npx exec processes are left running after foreman exits

[davetron5000]

web: PORT=6502 bin/run
sidekiq: bin/run-sidekiq
css: SHELL=/bin/bash npx chokidar --initial -p "app/src/front_end/css/**/*"    -c "bin/build-assets css"
js: SHELL=/bin/bash npx chokidar --initial -p "app/src/front_end/js/**/*"     -c "bin/build-assets js"
images: SHELL=/bin/bash npx chokidar --initial -p "app/src/front_end/images/**/*" -c "bin/build-assets images"

When I Ctrl-C foreman, bin/dev (and whatever it starts) and bin/run-sidekiq (and whatever it starts) terminate normally. The other commands do not and remain running.

When trying those on the command line, they do terminate when given SIGTERM. What's interesting is that Ctrl-C does exit those, but using KILL -INT does not.

Any ideas how to debug what is going on?