# Box border lines not showing properly on PDF

I have the following code that generate a box with text content:

\documentclass{report}

\usepackage{color}
\usepackage{lipsum}
\newcommand\tipbox[1]{%
\begin{center}%
\fcolorbox{black}{white}{%
\begin{minipage}[t]{\dimexpr\textwidth-2\fboxsep-2\fboxrule}%
#1%
\end{minipage}}%
\end{center}}

\begin{document}
\lipsum[1]
\tipbox{\lipsum[1]}
\lipsum[1]
\tipbox{\lipsum[1]}
\end{document}


However, in the generated PDF, it does not show the lines properly at 100% zoom. See the screenshots taken from Foxit Reader (note missing left border):

and from TeXworks reader (note missing top border):

If I increase the zoom to a larger number I can see all the lines. I haven't tried to print to see the results. Is this a PDF reader issue or a problem with my box? How to fix this?

-
Seems like a problem of the pdf viewer. Evince is doing fine, in Acrobat Reader (Linux version), the different edges are displayed at different zoom levels. –  Caramdir Feb 22 '11 at 20:49
@Caramdir Hi, the problem occurs at 100% zoom or less. With more than 100% they show all the lines. –  Weslei Feb 22 '11 at 21:11
@Caramdir: technically evince is doing wrong and acrobat is correct. The rasterization rules for PDF are counterintuitive. –  Lev Bishop Feb 22 '11 at 21:55

Change \usepackage{color} to \usepackage{xcolor} or for even better results (the lines meet properly in the corners of the box at all zoom levels) \usepackage[xcdraw]{xcolor}.