My site's 70 static html pages have always been indexed...however, my blog pages appear to be made of rubber, in one day then out the next. My blog is only about 170 pages and a few months ago only 145 pages were indexed, but slowly all 170 were included. A month or so later the number of indexed pages has dropped to only 65!
No messages in WMT, no hint whatsoever. Did they release another page eating animal? If it's the hummingbird, then it's aptly named, fast moving and eating many thousands of calories per day.
Is your site structure such that you can do a site: search for just your blog posts? The reason I ask is that often over the years I have seen a low number of pages listed as indexed in GWT, but as far as I could tell all the pages actually WERE in the index and could be seen with site:
It's funny though, a few weeks ago those pages were indexed. G shows the total number of pages indexed, but they don't list which are indexed or which are not (unless I'm missing something somewhere, any advice is welcome). Otherwise it's a lengthy process of elimination.