This glitch can be reproduced but results will be different each time.

Glitch Summary: When droppers are aligned together and hit with a redstone pulse without any tick delays, the item they transport will travel differently each time.

To Reproduce: Start with a system like below. The comparators are to show where the item is currently at. All of the droppers are facing left. Put any item in the right-most dropper. Hit the button. The item may either travel to the next dropper, skip a dropper and go to the third dropper, or not travel at all. For each setup, the travel path seems to be identical. If a new setup is created, the path will be different, however.