I don't have a tuner for my MKII (which is all I had when I was in the UK) but here is how my Alpine used to work.

If you were listening to a local radio station before switching sources and you have TA turned on then the HU would switch back when that station transmitted TA info.
If you were listening to a national (BBCR1 in my case) station then it would flick to ANY of the local BBC stations in the area transmitting TA info (I guess overlaying the TA info and the local station frequency on the R1 frequency) this meant being near the edge of several stations meant almost constant TA info.

Just what I used to see, and may explain things depending on what you have your tuner set to, rather than what SW version you have.