Latex inserts blank line AND indents new paragraph

Question

I'm very new with LaTeX. My setup is as follows:

\documentclass{llncs}
\usepackage{makeidx}
\usepackage{listings}
\usepackage{graphicx}
%the above just for the case that it is relevant to the problem

\section{Introduction}

FIRST PARAGRAPH

SECOND PARAGRAPH

THIRD PARAGRAPH

Nth PARAGRAPH

\section{Next-Section}

Between each paragraph I got just one blank line. Let every paragraph be the sentence "Nth blue bird." The problem now is that the output is formatted like so:

First blue bird
    Second blue bird

    Third blue bird

    Nth blue bird.

I.e. the second paragraph is just indented as I want it to be. But every consecutive paragraph is not only indented but also has a blank line inserted before.

Note that if I shorten the third paragraph the problem vanishes. (I did not check though if shortening of other paragraphs yields the same result).

Any idea? (Impeding deadline; Quick help is highly appreciated)