I have been having the same issue, emailed trainingpeaksabout it and they are looking into it but no idea if it is on their end or withings/nokias end. There is also another thread on here where some people are having the same issue with scale reporting incorrect weight/bmi to trainingpeaks.
Hopefully it gets fixed because its really annoying to have to go and manually correct this each day.
Edit: According to that thread withings has found the bug and will be releasing an update in the near future to fix it.