pages dropped when new pages added

[marigot]

The strangest thing happened to one of my websites this week. I had a small site with about 20 pages. All pages have been indexed for about 8 months.

Then recently I added 5 more pages of my own articles. Because the articles were in the same topic but not exactly the same niche, I placed them in a folder with their niche name.

I linked to the homepage of that niche from one of my blogs. The new pages were indexed immediately but now the old ones are gone except the index page.

I can't understand why the old ones would go and only the new ones would stay????