Bert,
The term "Dirty" is Jon's description of a chart to which an entry has been made to any field.
I find it hard to believe that you have not lost a chart in seven years but that's great. Maybe I am missing something basic...
I have just spent 20 minutes placing a chart in my inbox, opening it without changing anything (a non-dirty chart) and then closing. Half the time it is in the deleted folder the other half it isn't.
I will do further research. Any one else dropping notes?