this.isRTL is not a function error when using paper-dropdown-menu webcomponent

Question

Getting this error when loading up the paper-dropdown-menu webcomponent.

Uncaught TypeError: this._isRTL is not a function

Longer stacktrace for SEO:

Uncaught TypeError: this._isRTL is not a function get _localeHorizontalAlign @ iron-dropdown.html:306_updateOverlayPosition @ iron-dropdown.html:461_positionTargetChanged @ iron-dropdown.html:405_observerEffect @ polymer.html:1562_effectEffects @ polymer.html:1405_propertySetter @ polymer.html:1389setter @ polymer.html:1468attached @ iron-fit-behavior.html:222_invokeBehavior @ polymer-micro.html:433_doBehavior @ polymer-micro.html:426(anonymous function) @ polymer-micro.html:210_makeReady @ polymer-micro.html:111(anonymous function) @ polymer-micro.html:117 polymer-mini.html:2046 Uncaught TypeError: Cannot read property 'getWidth' of undefined(anonymous function) @ app-drawer-layout.html:189complete @ polymer-mini.html:2085Debouncer.boundComplete @ polymer-mini.html:2062_atEndOfMicrotask @ polymer-mini.html:2040window.MutationObserver.observe.characterData @ polymer-mini.html:2055

Answer 1

Apparently Polymer 1.5 is not compatible with paper-dropdown-menu version ~1.2.1. I had to downgrade to Polymer 1.4 to use the paper-dropdown-menu.

Edit:

The problem was the this component is not compatible with the Shadow DOM.