The solution to the leap year problem I found was to change 02/29/YYYY to 02/28/YYYY. This is not a perfect solution, but it was the only thing I could think of.

Here is the foreign key I made to join to the calendar table

date_fk = 
IF(
    [Date].[MonthNo] = 2
    && [Date].[Day] = 29
    ,DATE([Date].[Year],2,28)
    ,[Date].[Date]
)

I welcome anyone to come up with a "solution" that does not require me to alter the data in the table. If anyone knows how to do this within a cumulative total measure itself that would be better.