Why are Ulimit Soft Limits Ignored

I am doing some programming, and I want to have core dumps disabled by default and only enabled when the soft limit is increased using ulimit -c unlimited. I am trying to disable core dumps by default by having the following settings in the /etc/security/limits.conf file:

*               hard    core            unlimited
*               soft    core            0

After restarting and logging in, core dumps are still generated despite the fact that running ulimit -c gives 0. Setting the hard limit using ulimit -Hc 0 disables the core dumps, but I would like to use soft limits to disable core dumps. I would like to know why soft limits are being ignored in this case, and how to enforce these soft limits.