App appears to raise the temperature on its own!

[Gazza]

So....I'm getting a bit fed up with the system I have. I have a hub, a room thermostat and rad valves. I will often only heat parts of the house, controlled by the room stat in one of the rooms. I will often boost the heating when I want it via the app rather than using the schedule. 

I also go away for work for short periods when I don't want any heating in the house and so I set the temp to a low value (5.5 deg) and the 'Follow schedule' option off. But I have found, on several occasions - the latest just today - that the room stat is set to a 'high' temperature when I am away. I have wondered whether I have set the thing by mistake myself. BUT on this occasion I am absolutely certain that it is not something that I have done. As I left home three days ago I checked all the settings and the temperature set for the room stat was 5.5deg. This evening I looked at the app and the room stat was set for 17.5 deg - so I may well have been heating half an empty house for the last three days. I don't call that a very smart system!

Does anyone else experience this behaviour from the app or other parts of the system? Can anyone explain what is going on?

Many thanks for any input.