WMI query like returning different results than =

i have following 2 wmi querys biztalk 2006 r1. difference like replaced =

public void messages(string instanceid)

{

dataset messages = null;

querywmi querywmi = new querywmi();

// get the messages related to a particular service instance

messages = querywmi.query("select * from msbts_messageinstance where serviceinstanceid like '" + instanceid + "'");

dataset messagestest = querywmi.query( "select * from msbts_messageinstance where serviceinstanceid = '" + instanceid + "'" );

try

{

if( messagestest.tables[0].rows.count != messages.tables[0].rows.count)

{

messagebox.show( "different count" );

}

}

catch( exception exc)

{

messagebox.show( common.parseexception(exc) );

}

}

the instance id is

instanceid = "{b0099eac-87f7-4e54-b538-5f7a73d72d48}";

even though same code run against following 2 querys , should return same values first 1 (the like) returns more records.
the instanceids same , should returned second query.

in example i've given 4 records returned query , 2 = query.

looking @ returned value's serviceinstanceid values {b0099eac-87f7-4e54-b538-5f7a73d72d48}.

i want able use = since runs faster.

anyone able shed light this?


ps.
here code run

managementobjectsearcher managementsearcher = new managementobjectsearcher("root\\microsoftbiztalkserver", query);

managementobjectcollection managementobjectcollection = managementsearcher.get();

os running on? "like" supported in wmi on xp , server 2003 according to http://www.microsoft.com/technet/scriptcenter/resources/wmifaq.mspx. wonder if wmi engine might including more results query because has reinterpret query , gets duplicates?

i try adding distinct keyword query clause make "select distinct serviceinstanceid ..." query see if same results = one.

thanks,

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