strange drop down list behavior

I have an employee database with some drop down lists that allow selection of the department and position of the employees. The Department and Position value lists are sourced from related tables. I'll use the department field for the sake of discussion here. I am displaying the auto entered ID with the department name in the drop down list (ie, "25 Accounting") but saving only the record ID of the selected department in the employee record.

This is using the technique of having the drop down list on my layout, only 1 pixel wide with a related field next to it that displays the name of the department. The Department name field is a button that "Goes to" the drop down field.

The selection of departments works just fine but for some reason the drop down list is displayed far below the hidden (1px) field...half way down the page. But it's not consistent. For new records it displays correctly, For existing records being modified, it displays approx 15 px too low. But for records that have been previously created but the department never filled in. The drop down displays around 50px too low. Very strange.

Anyone every run into something like this?

Thanks in advance.

RDW