Index: app/views/common/_calendar.html.erb
===================================================================
--- app/views/common/_calendar.html.erb	(revision 18572)
+++ app/views/common/_calendar.html.erb	(working copy)
@@ -13,7 +13,7 @@
 <p class="day-num"><%= day.day %></p>
 <% calendar.events_on(day).each do |i| %>
   <% if i.is_a? Issue %>
-  <div class="<%= i.css_classes %> <%= 'starting' if day == i.start_date %> <%= 'ending' if day == i.due_date %> tooltip hascontextmenu">
+  <div title="" class="<%= i.css_classes %> <%= 'starting' if day == i.start_date %> <%= 'ending' if day == i.due_date %> tooltip hascontextmenu">
   <%= "#{i.project} -" unless @project && @project == i.project %>
   <%= link_to_issue i, :truncate => 30 %>
   <span class="tip"><%= render_issue_tooltip i %></span>
Index: lib/redmine/helpers/gantt.rb
===================================================================
--- lib/redmine/helpers/gantt.rb	(revision 18572)
+++ lib/redmine/helpers/gantt.rb	(working copy)
@@ -926,6 +926,7 @@
           style << "width:#{coords[:bar_end] - coords[:bar_start]}px;"
           style << "height:12px;"
           output << view.content_tag(:div, s.html_safe,
+                                     :title => "",
                                      :style => style,
                                      :class => "tooltip hascontextmenu",
                                      :data => data_options)
Index: public/javascripts/application.js
===================================================================
--- public/javascripts/application.js	(revision 18572)
+++ public/javascripts/application.js	(working copy)
@@ -1008,6 +1008,20 @@
     });
 });
 
+$(function () {
+  $('.tooltip').tooltip({
+    tooltipClass: "white-tip",
+    position: { my: "left top", at: "left bottom" },
+    open: function (event, ui) {
+      ui.tooltip.mouseover(function(){ui.tooltip.stop().animate({opacity:'100'})})
+      ui.tooltip.mouseout(function(){ui.tooltip.stop().hide("fade")})
+    },
+    content: function() {
+      return $(this).children(".tip").html();
+    }
+  });
+});
+
 function inlineAutoComplete(element) {
     'use strict';
     // do not attach if Tribute is already initialized
Index: public/stylesheets/application.css
===================================================================
--- public/stylesheets/application.css	(revision 18572)
+++ public/stylesheets/application.css	(working copy)
@@ -1044,38 +1044,6 @@
 table.cal .starting.ending a.issue, p.cal.legend .starting.ending {background: url(../images/bullet_diamond.png) no-repeat -1px -2px; padding-left:16px;}
 p.cal.legend span {display:block;}
 
-/***** Tooltips ******/
-.tooltip{position:relative;z-index:24;}
-.tooltip:hover{z-index:25;color:#000;}
-.tooltip span.tip{display: none; text-align:left;}
-.tooltip span.tip a { color: #169 !important; }
-
-.tooltip span.tip img.gravatar {
-  float: none;
-  margin: 0;
-}
-
-div.tooltip:hover span.tip{
-display:block;
-position:absolute;
-top:12px; width:270px;
-border:1px solid #555;
-background-color:#fff;
-padding: 4px;
-font-size: 0.8em;
-color:#505050;
-}
-
-table.cal div.tooltip:hover span.tip {
-  top: 25px;
-}
-
-img.ui-datepicker-trigger {
-  cursor: pointer;
-  vertical-align: middle;
-  margin-left: 4px;
-}
-
 /***** Progress bar *****/
 table.progress {
   border-collapse: collapse;
@@ -1431,6 +1399,7 @@
   color: #1D781D;
   border: 1px solid #1D781D;
 }
+
 /***** Tooltips *****/
 .ui-tooltip {
   background: #000;
@@ -1441,6 +1410,26 @@
   box-shadow: none
 }
 
+.ui-tooltip.white-tip {
+  color: #000;
+  background: #fff;
+  border: 1px solid lightgray;
+  box-shadow: 2px 2px 2px gray;
+}
+
+.tooltip{z-index:24;}
+.tooltip span.tip{display: none;}
+
+table.cal div.tooltip:hover span.tip {
+  top: 25px;
+}
+
+img.ui-datepicker-trigger {
+  cursor: pointer;
+  vertical-align: middle;
+  margin-left: 4px;
+}
+
 /***** Icons *****/
 .icon {
   background-position: 0% 50%;
@@ -1572,11 +1561,6 @@
   border-radius: 20%;
 }
 
-div.issue img.gravatar {
-  float: left;
-  margin: 0 12px 6px 0;
-}
-
 div.gravatar-with-child {
   position: relative;
 }