What version of iPhoto are you using?
With iPhoto 11 when you select a photo and select the Show Title Slide option the title of the slideshow is presented over the first slide in the slideshow, not the slide you were viewing when the check box was selected. The order of the slides is not not changed. The thumbnails all move one position to the right as the title indicator is added before the first slide in the series.
Just click on any photo, bring up the Settings pane and uncheck the Show Title Slide option. That will remove the title from the first slide.
If you want to make a title/description slide, create it in any text editor or layout application, i.e. Pages, and then do a Print ➙ PDF ➙ Save PDF to iPhoto. This creates a JPEG image of the document and imports it into iPhoto where you can add it as a separate slide in the slideshow.
OT