Tuner conflict

[Ghost Protocol]

Hi, got Vu+ Duo2 with each tuner configured on diseqc A/B; got Astra 28.2 on (A) and Hotbird 13 on (B), both tuners work perfectly independently, but when both tuners are running and I record a programme the other tuner doesn't seem to kick in to allow me to watch a different channel, any ideas why not?

Thanks.