Index: src/wp-content/themes/twentyfifteen/js/functions.js
===================================================================
--- src/wp-content/themes/twentyfifteen/js/functions.js	(revision 30567)
+++ src/wp-content/themes/twentyfifteen/js/functions.js	(working copy)
@@ -74,8 +74,10 @@
 						topOffset = ( $sidebar.offset().top > 0 ) ? $sidebar.offset().top - adminbarOffset : 0;
 						$sidebar.attr( 'style', 'top: ' + topOffset + 'px;' );
 					} else if ( ! bottom && windowPos + windowHeight > sidebarHeight + $sidebar.offset().top ) {
-						bottom = true;
-						$sidebar.attr( 'style', 'position: fixed;bottom: 0;' );
+						if ( $document.height() != sidebarHeight ){
+							bottom = true;
+							$sidebar.attr( 'style', 'position: fixed;bottom: 0;' );
+						}	
 					}
 				} else if ( windowPos < lastWindowPos ) {
 					if ( bottom ) {