In the following file:
http://dev.colincowie.com/assets/bootstrap/css/bootstrap.css
starting at line 4297 you have the following rule:
.nav > li:hover ul {
display: block;
}
This rule is not part of the original Bootstrap CSS (even for v3.0.0 that you seem to be using) and I am not sure why it’s there for you, but basically you will need to remove it and it should all work fine.
Cheers!