iOS7.06, TomTom and charge/deplete issue

I use TomTom sat nav quite a lot and it's been fine on earlier iOS versions and on a 4, 4s and now 5s. OK the phone gets pretty warm during guidance when plugged into the charger but all has been well. Until iOS7.0.6.

Now the 5s get really hot during charge/navigation and I notice also that the device now discharges despite showing it is charging when TomTom is running. The 5s lost 10% capacity whilst charging/running TomTom yesterday. Turning the app off allows the device to start to charge again and the heat disappears.

Anyone else seen this?