Hey Greg,
I would double check how many items your able to see, or how many items are on the table your using for the dropdown. You can double check how many items your seeing by adding the RecordID to the dropdown column. You are currently not able to limit your dropdown, as soon as your list goes over 50, you get a second page in the dropdown.
The dropdown list is hard coded to only show 50 entries at a time. This is because the longer the list, the longer it will take to load. If you created a dropdown of your customers, the list could swell up to 4000 entries. What we did do is make it so that you can type a customer name and the dropdown will filter its results as you enter each letter.
Hope this helps.