Version: (using KDE 4.3.2) Installed from: openSUSE RPMs Bug 211828 suggests that the thin lines that separate two connected tiles are a "feature" that should be configurable. Actually, this has never been a feature, but a rendering error. I've now grown accustomed to it, but I still try to kill it every now and then (since one and a half year, without any success).
Naively perhaps, this might be related to a similar problem KGoldrunner had, where all tiles unexpectedly received an unpainted outline-area after a new version of Qt 4 came out. The solution was to get the bounding QRectF of the pixmap and use QRectF::adjust to add 0.5 of a pixel on all four sides before rendering the graphics object into it. See trunk/KDE/kdegames/kgoldrunner/kgrtheme.cpp at KGrTheme::loadGraphic() for details.
@Ian: Nope, QGraphicsPixmapItem does that automatically. Because the pieces are not layed out relative to each other, but relative to the top-left corner to the puzzle, such an outline should not cause any problems.
SVN commit 1045065 by majewsky: Finally fix the ugly-lines-between-pieces bug: I forgot that QPens are cosmetic by default. BUG: 211873 M +1 -1 slicer-jigsaw.cpp WebSVN link: http://websvn.kde.org/?view=rev&revision=1045065