Network Activate only creates a single ‘pm’ table prevening plugin to function

On a multisite installation, when I network activate this plugin, only a single wp_pm table is created but the plugin is trying to access the wp_{blogid}_pm and hence will not read or send messages.

The fix is to change all references of $wpdb->prefix to $wpdb->base_prefix and the plugin works as intended for network activation. Otherwise the plugin should be activated per sire and not network wide.