PGFPlots - no lines between marks

Question

I am starting playing with plots in latex.
In my preample I have:

\usepackage{pgfplots}
\pgfplotsset{width=12cm,compat=1.9}

My plots code: (first is copy from from tutorial, second is my attempt)

\begin{tikzpicture}
    \begin{axis}[xlabel=Cost,ylabel=Error]
    \addplot[color=red,mark=x] coordinates {
    (2,-2.8559703)
    (3,-3.5301677)
    (4,-4.3050655)
    (5,-5.1413136)
    (6,-6.0322865)
    (7,-6.9675052)
    (8,-7.9377747)
    };
    \end{axis}
\end{tikzpicture}
\begin{tikzpicture}
    \begin{axis}[ymin=0, ymax=12, xtick={25,50,75,100,125,150}, grid=major, xlabel=x label,
    ylabel=ylabel]
    \addplot[color=blue,mark=x] coordinates {
    (25,1)
    (50,1.87)
    (75,2.79)
    (100,3.78)
    (125,4.83)
    (150,5.83)
    };
    \addlegendentry{legend 1}
    \addplot[color=black,mark=o] coordinates {
    (25,1)
    (50,2.91)
    (75,4.27)
    (100,5.91)
    (125,7.82)
    (150,9.00)
    };
    \addlegendentry{legend 2}
    \end{axis}
\end{tikzpicture}

And result:

My question is: Why my plot do not have line between ticks? Am I missing something?

EDIT:

I am using Ubuntu 13.10 with Kile 2.1.3. I downloaded PGFPlots 1.9 from sourceforge and pointed TEXINPUTS system variable to its location.
I am posting full document. It produces pdf with content identical to image posted above. First plot has lines between marks, second does not. (preamble is pretty large, because it will be my master thesis)

\documentclass[a4paper,oneside,12pt]{report}

\usepackage[OT4]{polski}
\usepackage[utf8]{inputenc} 

\usepackage{graphicx}
\usepackage{setspace}
\usepackage{indentfirst}
\usepackage{titlesec}
\usepackage{nameref}
\usepackage{zref-user,zref-lastpage}
\usepackage{fancyhdr}
\usepackage{listings}
\usepackage{enumerate}
\usepackage{pgfplots}
\pgfplotsset{width=12cm,compat=1.9}

%listings configuration
\lstset{
language=SQL,
basicstyle=\small\sffamily,
numbers=left,
numberstyle=\tiny,
frame=tb,
columns=fullflexible,
showstringspaces=false
}

\onehalfspacing
\titleformat*{\section}{\normalsize\bfseries}

\setlength{\parindent}{1cm}

\begin{document}
\pagestyle{plain}

\begin{tikzpicture}
    \begin{axis}[xlabel=Cost,ylabel=Error]
    \addplot[color=red,mark=x] coordinates {
    (2,-2.8559703)
    (3,-3.5301677)
    (4,-4.3050655)
    (5,-5.1413136)
    (6,-6.0322865)
    (7,-6.9675052)
    (8,-7.9377747)
    };
    \end{axis}
\end{tikzpicture}

\begin{tikzpicture}
  \begin{axis}[ymin=0, ymax=12, xtick={25,50,75,100,125,150}, grid=major, xlabel=x label,
ylabel=ylabel]
    \addplot[color=blue,mark=x] coordinates {
    (25,1)
    (50,1.87)
    (75,2.79)
    (100,3.78)
    (125,4.83)
    (150,5.83)
    };
    \addlegendentry{legend 1}
    \addplot[color=black,mark=o] coordinates {
    (25,1)
    (50,2.91)
    (75,4.27)
    (100,5.91)
    (125,7.82)
    (150,9.00)
    };
    \addlegendentry{legend 2}
  \end{axis}
\end{tikzpicture}

\end{document}