Not reproduced with Inkscape 0.48 and 0.48+devel r9812 on OS X 10.5.8 (both with cairo 1.8.10)
Please keep in mind that 'Cairo PNG' is an experimental Cairo surface, available in Inkscape for testing purposes of cairo-based export formats, and not intended to be used to export Inkscape SVG files to high-quality bitmaps (PNG): Use 'File > Export Bitmap' instead which deploys Inkscape's internal renderer.
When reporting bugs, there is no field to specify the version and the OS!
I'm using 0.48 on WinXP.