• Have just been hitting these problems in SSIS with Visual Studio 2015.

    Even though there is an 'Advanced Editor' which allows you to set the external datatypes to DT_NTEXT, this reverts to the detected type as soon as the window closes. Didn't try the registry hacks, just edited the first line of the spreadsheet to force correct datatypes.

    This also alphanumeric columns that just happen to have only numbers in the first few rows. SSIS helpfully detects these as floats or something.