Horizontal- and vertical-only shadows of a text frame in a PDF export are
displayed incorrectly in acroread 7 for GNU/Linux (KPDF displays them
correctly). Printing to .ps is affected apparently.

Steps to reproduce:

Start oowriter
Create a text document
Add a text frame
Go to context menu, Area
Choose Fill -> Color -> White
Choose Shadow -> [X] Use Shadow
Direct shadow to a single edge 
   (i.e. left, right, top or bottom, not a corner)
Export to PDF
View in acroread for GNU/Linux, current version is 7.0.8

=> the display renders artefacts, thin lines at unintended edges.

In the example (see below) a thin line is visible spanning the textframe at the
lower edge from the right edge minus the width of the shadow.

Further tests:

A sample .odp, .pdf and .ps and a .png screenshot of the incorrect render taken 
from acroread are at http://linuxfoo.de/tech/ooo/broken-shadow/

The same problem occurs for example with speech bubbles or pie charts at their
horizontal resp. vertical lines as well as for rectangular shapes.

Printed to file, the artifacts show in gs 8.15.3 (ESP Ghostscript) and gv 3.6.2.

The artifacts do not show in KPDF 0.5.4 (KDE 3.5.4). My theory is that KPDF
employs either adaptive or incorrect calculation.

Theory:

A calculation error during export to either PS or PDF renders unidirectional
shadows one pixel too tall/wide orthogonally to the direction of the shadow.
Thus, the shadow rectangle is becoming visible at unintended horizontal resp.
vertical edges of the frame.