fixes #9475

dist/css/bootstrap.css

@@ -3231,7 +3231,6 @@ button.close {
   padding-right: 15px;
   padding-left: 15px;
   overflow-x: visible;
-  overflow-y: auto;
   border-top: 1px solid #e6e6e6;
   box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.1);
   -webkit-overflow-scrolling: touch;
@@ -3257,6 +3256,10 @@ button.close {
   clear: both;
 }
 
+.navbar-collapse.in {
+  overflow-y: auto;
+}
+
 @media (min-width: 768px) {
   .navbar-collapse {
     width: auto;

less/navbar.less

@@ -51,20 +51,19 @@
 // content for the user's viewport.
 
 .navbar-collapse {
+  max-height: 340px;
+  overflow-x: visible;
   padding-right: @navbar-padding-horizontal;
   padding-left:  @navbar-padding-horizontal;
   border-top: 1px solid darken(@navbar-bg, 7%);
   box-shadow: inset 0 1px 0 rgba(255,255,255,.1);
-  // Clear floated elements and prevent collapsing of padding
   .clearfix();
-
-  // This is not automatically added to the `.navbar-fixed-top` because it causes
-  // z-index bugs in iOS7 (possibly earlier).
-  max-height: 340px;
-  overflow-x: visible;
-  overflow-y: auto;
   -webkit-overflow-scrolling: touch;
 
+  &.in {
+    overflow-y: auto;
+  }
+
   @media (min-width: @grid-float-breakpoint) {
     width: auto;
     padding-right: 0;