Lines, UV Mapping doubts.

[c-sanchez]

I'm practicing with the texturing, UV Mapping, although I seemed simple at first, I see some complicated things, or do not quite understand yet.

to explain to me better I'll will use an example with this "table"

A basic, simple, model


the problem(?) with smooth shading

why this happens?

on Ultimate Unwrap3D (3ds exported from Wings3D)

As far as I can assume, these lines should NOT appear.
the "squares" on top are simple extrudes.

As always, thank you very much for the help.