ipmt function ignorning the i argument?

[Marc Sherman]

I'm trying to create a scheduled transaction using the ipmt function to 
track the interest charges on my mortgage. I've got the function 
correctly calculating the interest for the first payment period, but it 
appears to be ignoring the "i" index variable, and recording the same 
interest value for every transaction.

Is there a trick to getting this to work?

Thanks,
- Marc