Normally speaking what happens when there are more then 1 egg in the cell is that the workers will get rid of the extras. However, it takes a while for the workers to catch up sometimes. That is why we can usually see that there are more then 1 egg. Now here is what you need to know as well.
1. Laying workers cause very spotty brood which is ALL drone.
2. Laying workers will normally have more then one egg in a cell but almost Always they will NOT be in the center of the cell but on the sides.
3. It is NOT uncommon to find more then 1 larva in the cell as sometimes the workers don't get rid of the extras.
4. If you are finding only drone brood, and only in actual drone cells, suspect a drone laying queen instead.