Additional Equipment Totals Incorrect

This may be user error.  I've never used the multi-select feature for equipment.

I just put new tires on my bike and want to track the mileage separately.  I went to the first day that I used them, which was last Sat.  I added the tires, and held the control key down to select the tires along with the bike.  I then went to Mon and Tue to do the same thing.  The total only included the ride on Tue and not the ones on Sat and Mon like I would expect.

Thanks for any help.