Pure Oasis DAB radio switches itself back on..

[punkieys17]

So with decent battery voltage the Pure Oasis digital radio will switch off....then with a modest delay will switch itself back on. The switch itself is a momentary push to connect and appears to be working correctly. Although a trained electronics engineer I last practised in the era of TTL so would appreciate any pointers to what I am looking for. My instincts are a capacitor breaking down - simply due to the delay.