I had a quick look at the game, found Yemandra's room at the keep and the events that check for quest 4. I assume that the other two events work the same way:
If you bring back the lance, an utilities events adds a value of 1 to quest 5.
Quest 5 keeps track of the number of retrieved arms.
There is a "quest stage" chained to the utilities event, which only fires if "stage 3" of quest 5 is reached - this is the event that will give you quest 4.
The way UA is designed, stage 3 in a "quest stage" event only fires if the particular quest has a value of 2.
That means if you have two of the items, quest 5 has a value of 2, thus the "stage 3" event fires and hands you the kidnap quest (4).
This was either meant to work that way, or the UA designers didn't really understand their own product (many mod-designers don't understand how the the "quest stages" events work at first, including me).
I've included a screenshot of the event in question. If you manage to find all three event chains where this particular event occurs, and change the "stage" of quest 5 from 3 to 4, the kidnapping should fire only after all three items have been recovered.
Do this at your own risk, however. I don't know what "side effects" this change might have.