Problems with date

I'm writing a client application in Visual Basic 5.0 on Informix On-Line 7.0 as database server on Unix/Senix. I'm using ODBC for interfacing. When i use a date in the "dd/mm/yyyy" format and "dd" > 12 then ODBC inverts month with days ("mm/dd/yyyy"). When "dd" <= 12 then sometimes ODBC inverts months with days but not always. I don't understand "WHEN" it inverts those fields. On the server DBDATE = dd/mm/yyyy. Thanks in advance...