Panel display query

Hello,

 I have a 2013 Fabia tsi 85 bhp. Just recently I have noticed something different. I first noticed it when I had filled up with petrol a couple of weeks ago now. When I switched on instead of the" miles left" om the display  I got 13 instead of the miles left. It stayed there for a few seconds then it changed to the normal display. I now notice it does it every time I switch on regardless. It stays on for 10 seconds at the most then changes to normal display. It  - bu but I could be wrong but I could be mistaken.never comes on when I am driving so I do not see how it can be a fault as such but I could be mistaken of course. The car is running perfectly, very good fuel consumption, no misfires, it pulls in high gear from low speeds,  its a mystery to me. 

       Can any Briskoda people out there tell me what this is and whether I need to do anything about it? The car is due for its 6 year fixed  service but "the service now" light and message hasnt come on in the display so I cant see it as being service related. I have looked in the handbook but cant see  any mention of this 13. I am planning on changing the car in the next few weeks or months so do not want a large bill, i would accelerate my plans for changing if that is the case. Could it be that the "days remaining to service"  has stuck at 13? It was definitely 13 showing last Friday, October 18th and its still 13 showing today, Wednesday October 23rd. I am beginning to think that is what is happening. If it is that will the "reset" done by the garage when they service the car sort this out?        Hope someone can inform me and put my mind at rest or, alternatively let me know if I am facing a totally unexpected bill.

                     Thanks in advance.,