Followup to PR #427 d74b70bb:

Copying timestamp of original css.tt2 confuses browser cache.  Older timestamp of css.tt2 should be avoided by measures in release and install process.

src/lib/Sympa/Upgrade.pm

@@ -1861,6 +1861,20 @@ sub upgrade {
         }
     }
 
+    # Clean style sheets with earlier timestamp so that they will be recreated
+    # with recent timestamp.
+    if (lower_version($previous_version, '6.2.41b.1')
+        and not lower_version($previous_version, '6.2.26')) {
+        if ($Conf::Conf{'css_path'} and -d $Conf::Conf{'css_path'}) {
+            my @robot_ids = Sympa::List::get_robots();
+            foreach my $robot_id (@robot_ids) {
+                my $dir = $Conf::Conf{'css_path'} . '/' . $robot_id;
+                next unless -e $dir . '/style.css';
+                unlink $dir . '/style.css';
+            }
+        }
+    }
+
     return 1;
 }
 

src/lib/Sympa/WWW/Tools.pm

@@ -790,7 +790,7 @@ sub _get_css_url {
         } elsif (
             (exists $hash{$lang || '_main'})
             ? ($hash{$lang || '_main'} eq $hash)
-            : ($template_mtime == Sympa::Tools::File::get_mtime($path))
+            : ($template_mtime < Sympa::Tools::File::get_mtime($path))
         ) {
             return ($url, $hash);
         }
@@ -894,8 +894,6 @@ sub _get_css_url {
 
         return;
     }
-    # Set mtime of source template to detect update of it.
-    utime $template_mtime, $template_mtime, $path;
 
     return ($url, $hash);
 }