Rails 3.0 + haml render partial ActionView::MissingTemplate

I'm upgrading one of my apps to rails 3.0

I get this error:
ActionView::MissingTemplate
Missing partial /layouts/header with {:formats=>nil} in view path

for:
= render :partial => "layouts/header"
the file is in views/layouts/header.

From the error message, it looks like it appends an absolute path: "/
layouts/header"

Anyone has seem this problem when upgrading to rails 3.0 pre?