${name} vs ${name-} with ${...//...}

[Lionel Cons]

Why do these two lines differ in output? ${name} and ${name-} should
produce identical output if "name" exists as variable, or not?

$  (name='bar" x' ; name="${name-//\"/}" ; printf "%q\n" "$name")
'bar" x'
$  (name='bar" x' ; name="${name//\"/}" ; printf "%q\n" "$name")
'bar x'

Lionel