On a Fedora 7 I have set following limits (only) on /etc/security/limits.conf:

*               soft    core            0
*               hard    core            32768

When I use bash I get this:

$ ulimit -Hc
32768

But with zsh I get this:

$ ulimit -Hc
65536

Reading the standards below it seems unambiguous that the correct block size
should be 512:

http://www.opengroup.org/onlinepubs/000095399/utilities/ulimit.html
http://www.opengroup.org/onlinepubs/009695399/functions/ulimit.html

However, http://ftp.gnu.org/gnu/bash/bash-3.2.tar.gz has the following in
bash-3.2/builtins/ulimit.def:

static RESOURCE_LIMITS limits[] = {
#ifdef RLIMIT_CORE
  { 'c',        RLIMIT_CORE,  1024,     "core file size",      
"blocks" },
#endif

Same goes for several other limits.

FWIW, zsh and ksh are using 512 and bash and tcsh are using 1024. I think bash
should be fixed. I'll open another case against tcsh.