<p dir="auto"><a href="http://twitter.github.com/bootstrap/components.html#navbar">This one.</a></p>
<p dir="auto">To reproduce it, change the width of your browser so you get the mobile/ipad dropdown menu. Click it, and then expand the window again so you get the standard bar. Now try to click either of the normal dropdowns, and it won't show at all.</p>
<p dir="auto">Not sure how common it is for users to do this, but the issue is definitely there.</p>
<p dir="auto">I had a play with .btn:hover combining the CSS3 Properties in mixins.less. I modified the button hover to add some wonky transforms to see what it would do. If I used one of the CSS3 properties the btn:hover displayed correctly, but the output css was really verbose/duplicated (see below). Adding two (say .skew &amp; .rotate) is where things got real... and by real I mean display only one of the transformative mixins and mangle the btn:hover css element.</p>
<p dir="auto">Also, the bootstrap.css -&gt; btn:hover element contains lots of  duplication as you can see below, and I am not sure what is going on there. I used less.app, crunch app and the regular less.js file to compile had the same output each time. Hopefully, I'm wrong and this is just my stupid error... but if not, I'd like at least 3 million dollars and a shot at the title.</p>
<p dir="auto">button.less:</p>
<p dir="auto">// Hover state<br>
.btn:hover {<br>
color: @grayDark;<br>
text-decoration: none;<br>
background-color: darken(<a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/white/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/white">@white</a>, 10%);<br>
background-position: 0 -15px;</p>
<p dir="auto">// transition is only when going to hover, otherwise the background<br>
// behind the gradient (there for IE&lt;=9 fallback) gets mismatched<br>
.transition(background-position .1s linear);<br>
.skew(-25deg);<br>
.rotate(9deg);</p>
<p dir="auto">// Also defined <a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/Degrees/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/Degrees">@Degrees</a> in the variables.less (same output, same problem)<br>
}</p>
<p dir="auto">The complied bootstrap.css for btn:hover looks like this:</p>
<p dir="auto">.btn:hover {<br>
color: #333333;<br>
text-decoration: none;<br>
background-color: #e6e6e6;<br>
background-position: 0 -15px;<br>
-webkit-transition: background-position 0.1s linear;<br>
-moz-transition: background-position 0.1s linear;<br>
-ms-transition: background-position 0.1s linear;<br>
-o-transition: background-position 0.1s linear;<br>
transition: background-position 0.1s linear;<br>
-webkit-transition: background-position 0.1s linear;<br>
-moz-transition: background-position 0.1s linear;<br>
-ms-transition: background-position 0.1s linear;<br>
-o-transition: background-position 0.1s linear;<br>
transition: background-position 0.1s linear;<br>
-webkit-transform: translate(-25deg, 0);<br>
-moz-transform: translate(-25deg, 0);<br>
-ms-transform: translate(-25deg, 0);<br>
-o-transform: translate(-25deg, 0);<br>
transform: translate(-25deg, 0);<br>
-webkit-transform: skew(-25deg, 0);<br>
-moz-transform: skew(-25deg, 0);<br>
-ms-transform: skew(-25deg, 0);<br>
-o-transform: skew(-25deg, 0);<br>
transform: skew(-25deg, 0);<br>
-webkit-transform: translate(-25deg, 0);<br>
-moz-transform: translate(-25deg, 0);<br>
-ms-transform: translate(-25deg, 0);<br>
-o-transform: translate(-25deg, 0);<br>
transform: translate(-25deg, 0);<br>
-webkit-transform: skew(-25deg, 0);<br>
-moz-transform: skew(-25deg, 0);<br>
-ms-transform: skew(-25deg, 0);<br>
-o-transform: skew(-25deg, 0);<br>
transform: skew(-25deg, 0);<br>
-webkit-transform: rotate(9deg);<br>
-moz-transform: rotate(9deg);<br>
-ms-transform: rotate(9deg);<br>
-o-transform: rotate(9deg);<br>
transform: rotate(9deg);<br>
-webkit-transform: rotate(9deg);<br>
-moz-transform: rotate(9deg);<br>
-ms-transform: rotate(9deg);<br>
-o-transform: rotate(9deg);<br>
transform: rotate(9deg);<br>
}</p>