Neither connectedCallback nor disconnectedCallback should be called when re-mapping causes a shuffle.

[theengineear]

Conceptually, if you render [foo, bar] and then re-render [bar, foo], neither of those elements should be disconnected at all. However, because low-level DOM apis will cause a disconnect followed by a connect — there’s no great way to perform this shuffle without causing at least one disconnection.

A new API is being proposed called moveBefore — whatwg/dom#1307. And, Chrome has begun implementing it — https://chromestatus.com/feature/5135990159835136. This should directly address the shuffle-disconnect issue.

[theengineear]

Note — we should look into adding a stub for connectedMoveCallback in the XElement base class once this all lands.