OCI recipe ARG variables break quoting

My recipe requires a variable to be given a value consisting of several space-separated values.

But setting a "Build-time ARG variable" with e.g.

FOO='bar baz bat'

is actually passed through as:

'--build-arg=FOO='"'"''"'"'"'"'"'"'"'"'bar baz bat'"'"'"'"'"'"'"'"''"'"''

Using no quotes at all is less broken, but still doesn't work:

FOO=bar baz bat

'--build-arg=FOO='"'"'bar baz bat'"'"''

I tried double quotes too for the sake of completion, but no joy:

FOO="bar baz bat"

'--build-arg=FOO='"'"'"bar baz bat"'"'"''

Ideally all of the above would do what was intended, but if quotes of some kind are going to be required, the exact syntax should probably be made explicit in the UI.