indyank - 3:32 am on Jul 3, 2013 (gmt 0)
Sorry i didn't notice that message earlier.
I changed the blue widgets page from blue-widgets.html to blue_widgets.html, without doing a 301 redirect.
Did you change the internal in-content links and navigational links to point to the new page?
Are the in-content links on pages which are topically closely related? How are those pages performing? Are they affected by any of these algorithmic animals?
Panda is a site wide algorithm. For penguin, Matt Cutts has addressed this question and I am sure he is right.
There was even a discussion thread here on the same topic.