The 'date' definition contains no time zone information. It is thus a floating date value and a health warning should be included about converting it to/from incremental time values.
This bug was cloned to create bug 17854 as part of operation convergence.
My plan is to prepare a change that adds a non-normative health warning. I'll start working on the change for HTML5.1 and if it is acceptable, I will port the change back to HTML5.0 CR branch and resolve this bug.
The health warning change has landed in 5.1. Please review:
Looks healthy to me.
(In reply to Addison Phillips from comment #4)
> Looks healthy to me.
Now back-ported to 5.0.
The I18N WG is also satisfied by this. Closing the related issue in tracker.