Mapping `<S-Space>` to `<Esc>` is not working

It looks like trying to set ShiftSpace to escape insert mode is not working. Visual Studio Code 1.13.1 on Mac OS X.

"vim.insertModeKeyBindings": [
    {
    "before":["<S-Space>"],
    "after":["<Esc>"]
    }
]

Update 1

Trying CtrlS to save file and escape insert mode, is not working either.

"vim.useCtrlKeys": true,
    "vim.insertModeKeyBindings": [
    {
        "before": ["<C-s>"],
        "after":["<C-o>:update<CR><ESC>"]
    }
]

Reproduce the mappings in Visual Studio Code on macOS, using the reported insertModeKeyBindings and useCtrlKeys settings. Trace how the extension handles Shift-Space and Ctrl-S in insert mode; done means the reported mappings consistently exit insert mode and perform the requested save behavior.