Two of same note playing at same time

I haven't found anything in the handbook on this (but perhaps I haven't looked carefully enough), but in any case, I have two notes that start on the same note (say, a D), in one voice the note changes after the first quarter note, but in the other voice it holds the D for several more beats. However, whenever two notes hit at the same time, the held note is always ignored after the first beat. How do I get the original note to keep on playing?

Thanks,
-Gidoza