Max-width of 400px for form-control class.

themes/bootstrap3/less/bootstrap.less

@@ -4,6 +4,7 @@
 .btn {&:extend(.btn-default all);}
 .fa-grid:before {content:"\f00a"}
 .fa-visual:before {content: "\f008"}
+.form-control {max-width:400px}
 .group [class^=col-] {padding-left:0}
 .highlight{&:extend(mark);}
 .icon-bar {background-color:#888}