Thank you for your post.
Can you be more specific about the tables being looked up. What are the names of the tables? What is the key field(s) being used? What is the field name and field type being referenced in the drop down? What options do you have set for the value list? Does this occur with a new file? If not, then try running Recover (File menu) on the database file and see if the recovered file exhibits the same problem.
Anything else you can provide to help me replicate the problem would be appreciated.