If you want to have the old behavior just add the following lines to your bootstrap-select.css:
.bootstrap-select.btn-group .dropdown-menu li > a {
display: block;
padding: 3px 20px;
clear: both;
font-weight: normal;
line-height: 20px;
color: #333333;
white-space: nowrap;
}
.bootstrap-select.btn-group .dropdown-menu li > a:hover, .bootstrap-select.btn-group .dropdown-menu li > a:focus {
text-decoration: none;
color: #ffffff;
background-color: #0081c2;
background-image: -moz-linear-gradient(top, #0088cc, #0077b3);
background-image: -webkit-gradient(linear, 0 0, 0 100%, from(#0088cc), to(#0077b3));
background-image: -webkit-linear-gradient(top, #0088cc, #0077b3);
background-image: -o-linear-gradient(top, #0088cc, #0077b3);
background-image: linear-gradient(to bottom, #0088cc, #0077b3);
background-repeat: repeat-x;
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ff0088cc', endColorstr='#ff0077b3', GradientType=0);
}