Stored Procedure quirks - Help!

I have problems with an existing stored procedure that just recently cropped up with a server change.  This is the sproc:

CREATE procedure usp_Comments1130
As
BEGIN
   
   
   INSERT INTO Comments1130 (ControlNo, SumAmt)
   SELECT  [Control #], Sum(Amount)
   FROM ODS_accounting_Schedule4 Left Join Comments1130 on ODS_accounting_Schedule4.[Control #] = Comments1130.ControlNo Where ods_accounting_schedule4.[Account #] = '1130' AND Comments1130.ControlNo Is Null
   GROUP BY [Control #]
   HAVING Sum(Amount) <> 0

   IF @@ERROR <> 0
   BEGIN
     RAISERROR('Insert into Comments failed', 16, 1)
     RETURN -1
   END  

 
   DELETE FROM Comments1130
   WHERE 0 = (
        SELECT SUM(Sched4.Amount)
        FROM ODS_accounting_Schedule4 Sched4
        WHERE Sched4.[Control #] = Comments1130.ControlNo
        AND Sched4.[Account #] = '1130'
   )


RETURN 0

END
GO

This seemed to be working fine (no reported errors before now) before a recent server change.  Now it doesn't actually give me the Sum(Amount) properly.  I'll post the data here for the specific control #'s that its fouling up:

Ctrl#         Acct#        Amount    Reference#
24122      1130      -50.0000      013004
24122      1130      -25.0000      032504
24122      1130      -25.0000      041504
24122      1130      500.0000      8470
25819      1130      -1250.0000      0425CASH
25819      1130      -800.0000      022404
25819      1130      -500.0000      032404
25819      1130      2500.0000      1055
26755      1130      250.0000      1073
26755      1130      500.0000      1084

There are only 4 control #'s in this table that have multiple entries.  The three above do not actually get sum'd up by the sproc correctly.  The only one that does is this one:

454593      1130      -150.0000      0216CASH
454593      1130      1400.0000      8470

I don't understand why it would work for '454593' and not the rest.  I need help cleaning this up because my reports based off this are now inaccurate!  Help!

Thanks.