I may be missing something, but I had an imported iCal trip last weekend that I can no longer find. My journal says, regarding this trip, "We imported a trip (since deleted) from an external calendar."
This seems like a problem, especially given your super awesome carbon calculator working on the basis of old trips. (I noticed this while trying out the calculator.)
Suggested behavior for trips imported from iCals: Once the trip starts, disconnect it from the iCal so that when it goes into the past and disappears from the iCal, it doesn't disappear from Dopplr.