Mail system causes a significant issue when using the Omega base theme.

Whenever I clear cache via the performance admin page it breaks the site (near WSOD except for logo/site name) which I then have fix by clearing the contents of the cache table in the database. At first I thought it was theme related but I managed to exclude that possibility by trying the theme (including subtheme) on a fresh Drupal install. I tracked this to Mail System by disabling all contribs and re-enabling them one by one. I tried reverting to Mail System 2.33 but that did not solve the issue.

I suspect Mail System somehow prevents the subtheme from using (preprocess) results from alpha, a component of the omega base theme. I confirmed that by copying a preprocess function into my subtheme's template.php. Solved the undefined rdf variable issue (but is not how the theme is designed to work).

Any ideas what may cause this?

Notice: Undefined index: highlighted in include() (line 124 of ...modules/system/page.tpl.php).
Notice: Undefined index: sidebar_first in include() (line 136 of ...modules/system/page.tpl.php).
Notice: Undefined index: sidebar_second in include() (line 142 of ...modules/system/page.tpl.php).
Notice: Undefined variable: doctype in include() (line 1 of ...omega/omega/templates/html.tpl.php).
Notice: Undefined variable: rdf in include() (line 2 of ...omega/omega/templates/html.tpl.php).
Notice: Trying to get property of non-object in include() (line 2 of ...omega/omega/templates/html.tpl.php).
Notice: Undefined variable: rdf in include() (line 2 of ...omega/omega/templates/html.tpl.php).
Notice: Trying to get property of non-object in include() (line 2 of ...omega/omega/templates/html.tpl.php).
Notice: Undefined variable: rdf in include() (line 3 of ...omega/omega/templates/html.tpl.php).
Notice: Trying to get property of non-object in include() (line 3 of ...omega/omega/templates/html.tpl.php).

Comments

I confirm disabling Mail System solves the issue .. not ideal :-s

Version:8.x-2.34» 7.x-2.34

Initially tagged with incorrect version.

I can confirm this as well.