d67f4f26ef
When the modal initially opens, the `#multiple` is `false`, (regardless of how it is configured), so the initial value is set to `[undefined]`. Then when the `#multiple` is observed as `true` (there must be an underlying bug with the modal context code here), then the `#selection` array already has an initial value of `[undefined]` so will append newly selected values to that array. I discovered this issue due to a bug with the Tree Picker editor.