Combo Box Menu Selection Problem

I am using a form with combo box selection menu. Sample Selections are ie:
Paper,Envelopes,Toner,Pouches . When the selection is made is filters and
opens a new form based on selection criteria. But after this process is
completed. I return to the Selection Menu and exit. Upon exiting the last
selection made changes the selection in the combo box.

This is a stand alone query/Table.

When I make a selection, the selected item is replace by the first choice in
the list.

Example: List selections, Paper, Envelopes,Seals,File Folder
After the selection of "Seals" the list is
"Seals,Envelopes,Seals,File Folder.


This code for the form filter

Dim stLinkCriteria As String
stDocName = "frmCategoryFormList"
stLinkCriteria = "[CategoryName]=" & "'" & Me![CategoryName] & "'"
DoCmd.OpenForm stDocName, , , stLinkCriteria

What am I doing wrong.