can.Observe.prototype.each overrides {{#each}} Mustache helper.

In Mustache.get (can/view/mustache/mustache.js line 822 in current HEAD) prototype functions and data members of the context object override Mustache helpers.  This causes the "each" helper to be unavailable when using a can.Observe, since its prototype includes "each", and an exception is thrown due to the two functions having different type signatures.