wp-columnize adding un-necessary tags

Wp-columnize is adding un-necessary <p> tags around the <div class=”column-sect”> or <div class=”post-column”> tags.

Typically my input is:

[col-sect]

[column] First col. [/column]

[column] Second col. [/column]

[/col-sect]

And the html generated is:

<div class="column-sect">
</p>
<p><div class="post-column">
<p> First col. </p>
</div></p>
<p><div class="post-column">
<p> Second col. </p>
</div></p>
<p>
</div>

I have tried doing my input both in the Visual and HTML mode of the editor, without any better result.