This was causing my error logs to fill up, so hope it is useful info:
in wp-cache-phase1.php
if ( isset( $wp_supercache_actions ) && false == is_array( $wp_supercache_actions ) )
return $value;
should be
if ( !isset( $wp_supercache_actions ) || !is_array( $wp_supercache_actions ) )
return $value;