ODBC issue with aggregate fields (SUM)

We do the following test on the client site :
A)Using SQLExecDirect with this query
------------
SELECT SUM("str_sls_totals"."strsl_net_dly"),
"dw_trans_type"."trans_type", "flash_dates"."year_number",
"flash_dates"."month_number", "flash_dates"."day"
FROM "dw_trans_type", "str_sls_totals", "flash_dates"
WHERE ("flash_dates"."dt" = "str_sls_totals"."strsl_per_dt") AND
("dw_trans_type"."trans_type" =
"str_sls_totals"."strsl_tran_type") AND
( NOT("str_sls_totals"."strsl_tran_type" IN (5,6)) ) AND
( "dw_trans_type"."trans_type" = 4 ) AND
( "flash_dates"."year_number" = 2005 ) AND
( "flash_dates"."month_number" = 8 ) AND
( "flash_dates"."day" = 13 )
GROUP BY "dw_trans_type"."trans_type", "flash_dates"."year_number",
"flash_dates"."month_number", "flash_dates"."day"
------------
Extract the column size with SQLColAttributes
SQLColAttributes:
In: hstmt = 0x00992148, icol = 1,
fDescType = SQL_COLUMN_DISPLAY_SIZE=6, rgbDesc = -892679478,
cbDescMax = 300, pcbDesc = -13622,
pfDesc = 0x00152C90, Description Type = SQL_C_SLONG=-16
Return: SQL_SUCCESS=0
Out: *pfDesc = 20
------------

So the size of SUM("str_sls_totals"."strsl_net_dly") is 20. When we
change the year to 2004 the size is returned as 30 ! ! ! Is this by
design or a bug.

Postgres 7.3.4, ODBC driver 7.3.200.

Thanks for any input you have.