I got similar problem with 64-bit version of tinycore downloaded from "ports" section. (corepure64 dated 11-May-2013, vmlinuz64 13-Nov-2012). I've used it to run distributed.net 64-bit client. I've successfully learned to boot tinycore to command prompt from both USB stick and as PXE boot. But when I run distributed.net client, it does not recognize Ctrl-C and could not be interrupted.
I've tracked it down to following. When client is run directly from command prompt, it works fine, and Ctrl-C interrupts. But if I'm using simple sh script to mount network (cifs) drive and run client in one command, Ctrl-C is NOT visible anymore. The only workaround currently found is to this run script in "current shell environment" using "." command:
. /mnt/sdb/startclient.sh
Only is this case Ctrl-C is passed to application. With any "standard" way to execute commands, like "/mnt/sdb/startclient.sh" or "sh /mnt/sdb/startclient.sh", which probably will load a new copy of shell - it does not.
For me, it look like something is wrong with BusyBox or it's signal handling in this setup.