When using the Autofilter feature, the drop down box displays records that are 
currently filtered out due to another field's autofilter selection.  For 
example if you create a new document with the following data:

Data1   Data2
1       1
2       2
3       3

Filter Data1 for 1, and the drop down for Data2 has all three choices even tho 
2 and 3 are already filtered out.  If you then filter Data2 for 2, no results 
are displayed.