The twitter card started working again and I forgot all about this. The post involved was (i think) http://www.pixel51.com/blog/archives/24344 but subsequent posts work fine and i assume the problem was corrected.
figured it out. Yoast SEO was the problem. Went to another plugin and it works now.
am using WP Mobile Detector plugin. That seems to be working. I can disable that, but what will happen with mobile devices?
