Issue #8569
According to the documentation (http://twitter.github.io/bootstrap/javascript.html#overview) the following code:
$('body').off('.data-api')
shall turn off JS plugins data-api functionality, but it doesn't.

This issue is reproducible on your site:
1. Open http://twitter.github.io/bootstrap/javascript.html#modals
2. Open browser's developers tools (usually, press F12)
3. Invoke the following JS code:
$('body').off('.data-api')
4. On the page in "Live demo" section press "Launch demo modal" button. Modal dialog appears, but according to documentation it shouldn't.
5. Try to invoke the following code:
$(document).off('.data-api')
6. Press "Launch demo modal" button => modal dialog doesn't appear.

Provided workaround:
Manually disabled body scroll bars when Modal is 'shown', enable them on 'hide' event