Drix,
Thank you for reporting this bug.
We have been able to reproduce this problem and it seems to be only an issue for user-defined graphs. In other words, built-in graphs like the weight and blood pressure graphs are smart enough to ignore blank values. Unfortunately, the user-defined graph code interprets blanks as if they were 'zero' values.
This will be fixed in a future release.
We're sorry for the issue and thanks again for bringing it to our attention.
Support Team