Default value from behavior lost when re-defining property on element

[kevinpschaaf]

Description

If a property is declared on a behavior to include a default value, and the property is also declared e.g. on the element (or any subsequent behavior) where the default value is not specified, the property will not be initialized. This is an unintentional compatibility change from Polymer 1.x.

Live Demo

3.x: https://jsbin.com/kuxoqig/edit?html,console,output
1.x: https://jsbin.com/puvowih/edit?html,console,output

Expected Results

Console logs "prop default value: 42"

Actual Results

Console logs "prop default value: undefined"

Browsers Affected

All

Versions

• Polymer: v2.x-3.x