What station are you listening to?

Local stations don't broadcast alternative frequencies in the RDS data - So what you're seeing is expected behaviour for a station like Q103.

Try Radio 1, or another national station. In programming and testing I used Radio 1 and Radio 4, both broadcast about 10 alternative frequencies. In the Cambridge area tune to 98.5 and the AF list should populate within a few seconds (providing your antenna is up to scratch).

Toby