As it was first said in the github issue tracker:
it would be nice if at the exit of the desktop app, it verify if the sync is completed. If not, you get a blocking popup asking something like : "Not all changes are synced. Do you want to wait for the sync to be completed?"
I think it is usefull so the user is warned and can make a choice.
Another idea would be to force a sync at the exit so the user does not have to make a choice and the data are always synced.