Z-index is set to 2 --> display issues with dropdowns

As the z-index is set to 2, the dropdown menus are displayed _under_ an input textfield

(see _bootstrap.scss :
.input-group .form-control {
        position: relative;
        z-index: 2;
        float: left;
        width: 100%;
        margin-bottom: 0;
    }
)