A question about ComboBox control in C# winform

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C#3.5

Hi every body,
I develop a windows form application, i use in a form 12 combobox controls
as follows
cmb1, cmb2, cmb3 are three combobox databonded to dt1 ( a datatable).
cmb4, cmb5, cmb6, cmb7, cmb8 are databonded to dt2 (a datatable).
cmb9, cmb10, cmb11, cmb12 are databonded to dt3 .
when running the project
when i select an item from cmb2 :
cmb3 and cmb1 change their items also but different columns, because they are bonded to the same datatable, until now every thing is good
when i just do a click on any other combobox say cmb5 :
cmb1 and cmb3 change the selected text although cmb1 and cmb3 are bonded to a different datatable.
How i make the selected text of a combobox does not change when i click or change the selected text of another combobox .

// Declare a datatable.
DataTable dt1=new DataTable();

// assign table tbl1 bindingsource to cmb1 as a datasource.
cmb1.DataSource=tbl1BindingSource;

// Declare datatable dt2.
Datatable dt2=new DataTable();
cmb2.DataSource=tbl2BindingSouce;

// Fill dt1 with some data from tbl1 using a stored procedure sptbl1 and dt2
// from tbl2.
dt1=sptbl1;
dt2=sptbl2;

tbl1BindingSource.DataSource=dt1;
tbl2BindingSource.DataSource=dt2;

this code is put in form_load event
in running the project when select an item from cmb1 then select an item from cmb2, cmb1 text change automatically, this is the problem.