pixeline on "WP Super Cache not working _ Debug mode shows nothing"

I noticed my homepage breaks if WP Super Cache's caching is activated. In the error_log i get this:

[14-Aug-2012 23:16:14] PHP Fatal error:  Cannot use object of type WP_Query as array in /domain/path/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 1154
[14-Aug-2012 23:16:14] PHP Fatal error:  Call to a member function get() on a non-object in /domain/path/wp-includes/cache.php on line 113

I guess it's probably related. I developed my own theme and have some custom loops on the frontpage. Could that be it?