Dev mode giving multiple errors but everything works
One of the things Dev Mode does is put Twig into a strict mode where it will throw an error any time a variable is referenced that isn’t defined. So that explains why you’re only getting these errors when Dev Mode is enabled. The errors should also show the part of your template code where the error occurred.

If you are certain that this is a bug, please send in a ticket from your Dashboard, including your DB backup and template files, so we can look into it.