After importing a particular power point document, I noticed that several images in the file appeared transparent in edit mode.  There were a few black squiggles and outlines (more than nothing), but not recognizable as the original image.

In Slide Show mode, however, all of the images were visible and rendered correctly.  From the editor, the non-visible images could also be saved as displayable images (right click on clear out line of image->Save As Picture-> select PNG format).  The default output format chosen for saving the non-displayed images was WMF (windows meta file).  Other displayed images had PNG chosen as the default output format.

The export of the file to PDF also did not render the images correctly.  

Here's a link to the example power point file where this was observed.  Take a look at slide #s 4,5,6,27, 28,and 29 in comparison to say slide 3, 9, and 20.

https://gridlab-d.svn.sourceforge.net/svnroot/gridlab-d/course/FourDayCourse/5.1%20-%20Market%20Module.ppt

This was observed with the just released Libreoffice 3.3 RC1 build.

For comparison, the same images/slides were rendered just fine with OpenOffice 3.2.1 Impress editor mode.