If I record ITV3 (C30- 545.8MHz, a low-ish powered SD mux @50kW) using tuner B, and record BBC1 SD (C22 482.0Mhz @150kW) on tuner C, there is interference on tuner B.
Tuner B works fine in isolation, and even when tuner C is recording an HD channel.
Any other combination of tuners seems to work ok.
One thing that caught me out was that different tuners get used when waking up from deep standby if the box doesn't drop back to standby during the recording(s) (as it should).