So it seems after some testing, and if the signal path is correct, that if you setup a new Tidal sub to the HiFi tier expecting lossless 44.1/16 FLAC then you’re going to be getting something other than you bargained for.
Whilst not completely consistent (some artists and albums behave differently to others), it does seem like the HiFi (non-MQA) tier can and does serve-up MQA streams. I asked the tester to repeat the tests with the infamous Led Zep MQA only catalogue and sure enough, he got spurious results:
Choosing the 44.1 MQA version of the first eponymous release, he got MQA and subsequent upsampling.
Choosing the 96 MQA version of the same release, he got 44.1 FLAC with no additional upsampling.