Suppose I have tasks A, B, C due today.
Suppose I have tasks A, B, C due today. And say B is a (daily) repeating task. The iCal entry for today will come up as A, B, B, C (duplication of B, the repeating task). You don't see the duplication in future entries until you get to that day. So say tomorrow I've got to do E and F (and B which is repeating daily). Then today I see my tomorrow's task as B, E, F but when I return to it tomorrow it will be B, B, E, F. So, long story short, you've got a bug on how the repeating tasks are being pushed into iCal.