Any Lightroom users out there?

How can I get consistent sharply rendered images in the Slideshow mode? Some images appear sharpen from the start of the slide show, some are sharpened during the slideshow, and some are shown with no sharpening at all. I have purged Lightroom's cache and also set the Preview Quality (under Catalog Settings) to "High" but the problem still presists. I get consistent results (sharp images) when I use the Bridge slideshow.

Any thoughts on how I can get Lightroom to show a decent Slideshow?