[AccessD] Bound combo is setting the value in the underlying record source's foreign key field to 0

I have a form where a combo is has bound column = 0, controlsource is my
field FKRetailerID in the table on which the form is based. The rowsource
is 

SELECT CompanyID, company FROM Company WHERE FKCompanyTypeID = 2 and
nz([deleted],"")="";

That is to give me a list of all companies of the required type (retailer)
which are not shown as deleted in the company table.

The filter for the form happens to be FKRetailerID = 2 but this is not
making a difference whether FilterOn is true or false.

The disruptive behavior is that whenever I position the combo on a value, it
shows a valid company name (Column 1 is ComnanyName) . But it is setting the
bound column's value to 0 in the data table.

Testing ?screen.activeform.controls("CBORetailer").Column(0) in the
immediate window, I can see the combo's 1st column has a value of 2.
Testing?screen.activeform.controls("CBORetailer").Controlsource I can see
FKRetailerID is the bound field.

However the underlying table is getting set to 0. 

This is maddening.

Help?!