Brown Box question.

My 9660 came with the original old Brown Box system and it actually works very well. However, mine has developed a rather annoying issue over the last few days.
Every time I restart the combine after it was shut down, for whatever reason, the Greenstar shows a ridiculous yield. Let's say I shut down in the evening, or even during the day and the yield shows 12 tons/ha average, it will show something like 70 tons/ha when I start up again. Ironically, it's only the weight that changes and not the area that was harvested.
I now write down and then clear the field totals every time before I shut down and then calculate each fields' total yield afterwards.
Anybody experienced this or know where the problem might lie?