atsamd: SPI IdleLow does not IdleLow

I am currently trying to drive the Circuit Playground’s Neopixels using SPI. For doing so @david-sawatzke started writing an experimental crate. However, while trying to use it, I noticed the first pixel to always display #008000 instead of #000000. As we were able to determine with a logic-analyzer, the reason is that the SPI is IdleHigh and this is being interpreted as the first bit being one (ws2812 uses green-red-blue). My code:

let mut peripherals = Peripherals::take().unwrap();
let core = CorePeripherals::take().unwrap();
let mut clocks = GenericClockController::with_internal_32kosc(
    peripherals.GCLK,
    &mut peripherals.PM,
    &mut peripherals.SYSCTRL,
    &mut peripherals.NVMCTRL,
);
let mut pins = hal::Pins::new(peripherals.PORT);

let spi_pinout = hal::sercom::SPI5Pinout::Dipo2Dopo2 {
    miso: hal::sercom::Sercom5Pad2::pb0(pins.foo, &mut pins.port),
    mosi: hal::sercom::Sercom5Pad3::pb23(pins.neopixel, &mut pins.port),
    sck:  hal::sercom::Sercom5Pad1::pb17(pins.bar, &mut pins.port),
};

let gclk = clocks.gclk0();
let spi = hal::sercom::SPIMaster5::new(
    &clocks.sercom5_core(&gclk).unwrap(),
    3_000_000.hz(),
    embedded_hal::spi::Mode {
        polarity: embedded_hal::spi::Polarity::IdleLow,
        phase: embedded_hal::spi::Phase::CaptureOnFirstTransition,
    },
    peripherals.SERCOM5,
    &mut peripherals.PM,
    spi_pinout,
);

let mut ws = ws2812_spi::Ws2812::new(spi);

(The pins pins.foo and pins.bar are PB0 and PB17 respectively, I just added them to get the SPI peripheral working …)

Is there something wrong on my side or is this an issue in the hal?