I have looked around and found the answer in Goossens et al, The LaTeX companion.
So, for future reference: The \twocolumn command in LaTeX never balance the
lines. To balance the lines the multicol environment has to be used.
In Preamble:
\usepackage{multicol}
And in ERT
\begin{multicols}{2}
then write the text
and at the end in a new ERT
\end{multicols}
And things are almost nice and balanced, at least it is a great step forward
from standard LaTeX.
Ingar
