PGF/TikZ arrow line width not consistent with line width

Question

I have a document I created several months back, and maybe with a new version of PGF/TikZ it is not working as previously (currently using Arch Linux, TexLive 2011, pgf version 2.10). The fast question is that I have a picture like this:

\begin{tikzpicture}[remember picture,overlay]
\draw [line width=4pt,->,line join=round,line cap=round,red!50] (tl2) -- (tl1);

where tl2 and tl1 are previously defined nodes. Line is displayed right, with a width of 4pt, but the cap is displayed as if the line had a smaller width, obtaining the following:

The question is, how can I get the tip of the same width as the line?

This may be related with this other question regarding line width in layers, but I'm not sure: Bug in TikZ? Line width on layers

EDIT:

I include minimal compilable code to show the behavior:

\documentclass[a4paper,12pt,oneside]{scrreprt}
\usepackage[left=2.5cm,right=3.5cm,top=3cm,bottom=3cm]{geometry}
\usepackage{tikz}

\begin{document}

I have ...

\begin{tikzpicture}[remember picture,overlay]
\coordinate[xshift=-1.8cm] (tl1) at ([yshift=-2cm]current page.north east);
\coordinate[xshift=-1.8cm,yshift=2cm] (tl2) at (current page.south east);
\draw [line cap=round,line width=4pt,->,red!50] (tl2)  -- (tl1);
\node [above,right=5pt,scale=.7,color=black!50] at (tl1) {timeline};
\end{tikzpicture}

\newpage

\end{document}

I use remember picture because I reuse the tl1 and tl2 nodes defined here.

SOLUTION:

Well, I found pdflatex fails with that rendering, but the combination, for example, of latex + dvipdf works as expected. I checked this with Ubuntu 11.10 and Arch Linux, both running TexLive 2011, so the problem may reside in the TL2011's pdflatex.

Answer 1

An minimal example, which shows a correct arrow tip:

\documentclass{article}
\usepackage{tikz}
\newcommand{\putnode}[2][]{\tikz[overlay,remember picture]{\node (#2) {#1};}}
\begin{document}
\putnode{tl1}

\vspace{2cm}
\putnode{tl2}

\begin{tikzpicture}[remember picture,overlay]
  \draw [line width=4pt,->,line join=round,line cap=round,red!50] (tl2) -- (tl1);
  \node [right of=tl1, color=gray] {\Large\textsf{timeline}};
\end{tikzpicture}
\end{document}​

Compiled also with TeX Live 2011 and pgf 2.10: