Ajax 3.5 causes incorrect autocomplete display

I have an issue with autocomplete on a TextBox in an aspx page.The method that gets the autocomplete list correctly returns a list of strings like in the 1st column (below), but when displayed, it looks like the 2nd column. Somehow some (most) of the strings are being changed. A "05" has been typed in the textbox to get the 1st column, so it must think that all the items that it is displaying start with 05.
Can you say what is happening here?
Note that the first column is debug output from the web method.

It appears to have become an issue when this:
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
was changed to:
<%@ Register Assembly="AjaxControlToolkit3.5, Version=3.0.20820.17273, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

The reference in the Visual Studio project is correct: "AjaxControlToolkit3.5"

Problem occurs in IE, Firefox, and Chrome.

The control in the aspx file:

<td style="width: 103px">
<asp:TextBox ID="txtDepartments" runat="server" MaxLength="10" Width="100px"></asp:TextBox>
    <asp:AutoCompleteExtender ID="AutoCompleteExtender2" runat="server" TargetControlID="txtDepartments"
        ServiceMethod="GetDepartments" EnableCaching="true" MinimumPrefixLength="2" CompletionInterval="100"
        CompletionSetCount="12" FirstRowSelected="true">
    </asp:AutoCompleteExtender>
</td>

Select allOpen in new window

0511000000  86245376
0511001000  86245888
0511002000  86246400
0511003000  86246912
0511004000  86247424
0511005000  86247936
0511007000  86248960
0511008000  511008000
0511009000  511009000
0511010000  86249472
0521000000  88342528
0521001000  88343040
0521002000  88343552
0521003000  88344064
0521004000  88344576
0521005000  88345088
0521006000  88345600
0521007000  88346112
0521008000  521008000  
0521009000  521009000
0521010000  88346624
0531000000  90439680
0531001000  90440192
0531002000  90440704
0531003000  90441216
0531004000  90441728
0531005000  90442240
0531006000  90442752
0531007000  90443264
0531008000  531008000
0541000000  92536832
0541001000  92537344
0541002000  92537856
0541003000  92538368
0541004000  92538880
0541005000  92539392
0541006000  92539904
0541007000  92540416
0541008000  541008000
0551000000  94633984
0552000000  94896128