Index: src/wp-admin/js/inline-edit-post.js
===================================================================
--- src/wp-admin/js/inline-edit-post.js	(revision 36260)
+++ src/wp-admin/js/inline-edit-post.js	(working copy)
@@ -50,6 +50,10 @@
 		// add events
 		$('#the-list').on( 'click', 'a.editinline', function( e ) {
 			e.preventDefault();
+			// Don't open a new Quick Edit form when a previous Quick Edit request has not completed yet.
+			if ( inlineEditPost.xhr && inlineEditPost.xhr.readyState !== 4 ) {
+				return;
+			}
 			inlineEditPost.edit(this);
 		});
 
@@ -264,8 +268,13 @@
 		fields = $('#edit-'+id).find(':input').serialize();
 		params = fields + '&' + $.param(params);
 
-		// make ajax request
-		$.post( ajaxurl, params,
+		// Abort the AJAX request if there's already one in progress.
+		if ( inlineEditPost.xhr && inlineEditPost.xhr.readyState !== 4 ) {
+			inlineEditPost.xhr.abort();
+		}
+
+		// Fire the AJAX request.
+		inlineEditPost.xhr = $.post( ajaxurl, params,
 			function(r) {
 				$( 'table.widefat .spinner' ).removeClass( 'is-active' );
 				$( '.ac_results' ).hide();