c8356e9 was meant to fix it, but it does not work.
When sourcing it from zsh, I get:
% source load_smartcd
+load_smartcd:3> [[ -n 5.0.6-dev-0 ]]
+load_smartcd:4> [[ '' != load_smartcd ]]
+load_smartcd:5> echo 'This cannot be run as a command, please run'
This cannot be run as a command, please run
+load_smartcd:6> echo
+load_smartcd:7> echo ' source load_smartcd'
source load_smartcd
+load_smartcd:8> exit 1
Maybe this was just taken from http://unix.stackexchange.com/a/73010/1920, or have you tested it?