RODBC: DNS vs. connection string

I am able to connect to an SQL Server Express 2005 instance using either
a local source or a connection string (i.e., the two forms of odbcConnect)
but sqlColumns returns different results. Specifically two string columns
are reported as being of type ntext and length 1073741823 in the first case
vs. nvarchar and 0 in the latter. Neither seems correct since in the schema
these two columns are declared as nvarchar(max). Does that ring a bell with
anyone?

Thanks,

-- O.L.