I realized that updating Panel could brake my site so I kept it to the release working for me (dev 2011.04.20) until yesterday when the update of Views and Date cause my site to display for each panel page a long list of errors like:

  • Notice: Undefined index: panels_stylizer_stylizer_style_render_pane in ThemeRegistry->resolveCacheMiss() (line 416 includes/theme.inc).
  • Warning: include(.tpl.php): failed to open stream: No such file or directory in theme_render_template() (line 1382 di includes/theme.inc).

So I decided to update panels to 7.x-3.x-dev (2011-Dic-07).
Now no more errors where displayed but panel pages where blank and the "Content" section of the panel editing didn't show nothing below "Substitutions": the different panes, that host the fields to be displayed, disappeared.

Clearing the cache solved the problem