I'm using your great plugin for a long time. A few days ago I've begun to test WordPress 3.9 on my testing server. And I see blank area in visual editor (in text editor everything is OK) when WP-Polls plugin is enabled. After disabling WP-Polls visual editor works fine.
I know that WordPress 3.9 is beta and not actual now but just wanted to let you know and help to be ready for the future WordPress Release.