In our testing of the SPWF04SA module in SPI mode, we've noticed that even when nCS is held high, the module is actively driving MISO low. Additionally, with nCS still high, when we clock SCK for another bus device, the SPWF04SA will actually send apparently valid data out on the MISO pin. MISO should never be driven by the SPWF04SA when it isn't selected. This interferes with other SPI devices on the same bus.
We've confirmed this by the fact that other bus devices again work correctly when holding the SPWF04SA in reset.