Word splitting problem on --gzip-options in auto/config

[Jason Heeris <jason.heeris@gmail.com>]

I am at a loss trying to explain this auto/config word splitting
behaviour. My auto/config contains only:

--
#!/bin/sh

set -e

GENERAL_BUILD_OPTIONS="--gzip-options '-9 --rsyncable' --security false"

lb config noauto ${GENERAL_BUILD_OPTIONS} "${@}"
--

(This is not my actual project, it's just a stripped down example.)
When I run "lb config" I get:

--
[2016-02-14 12:57:24] lb config
P: Executing auto/config script.
[2016-02-14 12:57:24] lb config noauto --gzip-options '-9 --rsyncable'
--security false
lb config: unrecognized option '--rsyncable''
--

My understanding of word splitting in POSIX was that the gzip options
here would be treated as a single argument.  I get the same error
running "dash auto/config". Of course, pasting that *exact* line "lb
config noauto ..." into my terminal and hitting enter works. What is
actually happening here?

This is on Debian Stretch, live-build 1:20151215 (5.0~a11-1).

Cheers,
Jason