Not sure what exactly might be causing this. One possible reason for it might be if you have added the “collapsed” class to your menu button link too – e.g.:
<a id="menu-button" class="collapsed"></a>
That link should look like this in your source:
<a id="menu-button"></a>
If this is not it, then I will need to look at some sort of live demo in order to investigate it so please provide such if possible.
