I've had the same problem with the Sybase DataDirect ODBC driver (I've resorted to re-preparing every SQL statement before every execute). For Oracle, I've used the "Oracle in OraClient10g_home1" driver (I haven't even tried the DataDirect driver for Oracle though I do have it) and I have no problems with your code (though you should think about using RaiseError in the connect).

Update: And ever since ActivePerl has started coming bundled with with the DBD::Oracle module (using the native Oracle driver rather than ODBC), I've used that with no issues also (though some things still use ODBC). And almut's workaround looks like it's worth a try though I don't know when or if I'll get around to trying it :-)