field splitting behavior

[Paul Lew - remove nospam when reply <paullew@xxxxxxxxxxxxxxxx>]

Take a look at the following:

> var='foo:bar' 
> echo ${(@)${(s/:/)var}[1]}
foo

> var='foobar'
> echo ${(@)${(s/:/)var}[1]}
f

So why it did field splitting on each character when there is no
separator ':' found?  I would expect 'foobar' on the output.

Thanks in advance..