iCal import trips automatically delete and re-add occasionally

I have a calendar import set up from Tripit, which works great, except . . .

Occasionally the trips that have been imported from my iCal get deleted and re-added. This only appears to happen when the link has not been broken by editing the trip in Dopplr. This started happening last Saturday and happened again this Saturday.

I didn't make any changes to my Tripit feed, though I suppose they could have reset something on there side.

This isn't exactly a problem for me, but I assume it also causes my trips to show up again in all of my contact's activity feeds. Not good :-(

Thanks,
Ethan