Redmine

I wrote a plugin for my company and
I referenced offical redmine plugin develop tutorial to add hook with my plugin.
I do something like this :

class MyPluginHook < Redmine::Hook::ViewListener
render_on :view_projects_show_left, :partial => "polls/project_overview"
end

It worked fined until I modified some features.
I got the information for log that this hook rendered two time
,so the whole page turn into a mess.
After restarting apache (I use apache 2.2 & passenger)
Everything is fined again, but sometimes it happened again.
By sometimes, this may happen after issue updating.