Excel 2007 : Gantt Chart Date

Hello. I am working on a project at work that involves me creating a gantt chart (or a modified bar chart) tracking dates. It is set up with eight stages, a start date for each stage entered as May 10, 2010, and then several extensions for each stage, which push the start date of each stage back. I have all of this figured out. My problem stems from the Gantt chart start date. If for example my start date is May 10, 2010, if I have a short completion date, say 20 days, the chart looks fairly accurate (It will start around April 30th). My problem comes when I have longer project timelines. If the project is due to run to the end of August, my graph now starts back in March. I'm not sure why this is happening.

I know this is a fairly confusing description, and I'm hoping that it is relatively clear what's going on. Please let me know if you need any further information.

Any help would be greatly appreciated!

Thanks.

I have now attatched the document.