Thread: Teak sideboard - what have I done wrong? Please help

You need to sand the complete door, otherwise you will have Danish oil on top of the old finish

I suspect the doors are a composite with teak veneer facing/edgings, rather than solid teak. If so, the face veneers would be quite thin initially and a subsequent light sanding could make them significantly thinner, bringing the glue layer much closer to the surface and affecting the way that the materials take up the Danish Oil. As mentioned above, if you don't evenly sand the entire surface, you won't get a consistent finish over the surface, as there will be more of the original finish in areas that were not sanded or very lightly sanded in comparison to the areas that needed the most sanding.