hero-transition -> core-header-panel with mode="cover" fails

It seems that a hero-transition from one animated page to one with a <core-header-panel mode="cover"> breaks the panel/toolbar.

I am able to reproduce the behavior with something like this:

<core-animated-pages id="controller" selected="{{selected}}" transitions="hero-transition">

  <section>
    <div class="container" hero-p>
      <div class="card" hero-id="hero" hero on-tap="{{transition}}">
        <div class="card-top" style="background:#000;" hero hero-id="bad">
        </div>
        <div class="card-bottom">
          <div class="card-title">
            HELLO
          </div>
          <div class="card-subtitle">
            WORLD
          </div>
        </div>
      </div>
    </div>
  </section>

  <section>
    <core-header-panel mode="cover">
      <core-toolbar id="core_toolbar" class="tall" hero hero-id="hero">

        <paper-icon-button icon="arrow-back" on-tap="{{transition}}"></paper-icon-button>
        <div flex>HELLO WORLD</div>
        <paper-icon-button icon="more-vert"></paper-icon-button>
      </core-toolbar>
      <section layout vertical fullbleed>
        <h1 style="color: #fff;" hero hero-id="bad">SAMPLE CONTENT</h1>
      </section>
    </core-header-panel>
  </section>

</core-animated-pages>

Here are some basic styles, perhaps something is conflicting, I don't know:

       core-animated-pages {
        height: 100%;
      }

      .container {
        position: absolute;
        top: 275px;
        left: 0px;
        right: 0px;
        text-align: center;
      }

      .card {
        display: inline-block;
        position: relative;
        border-radius: 3px;
        margin: 4px;
        overflow: hidden;
        text-align: start;
        background-color: #fff;
        box-shadow: 0 2px 10px 0 rgba(0, 0, 0, 0.16);
      }

      .card-top {
        width: 200px;
        height: 200px;
        text-align: center;
      }

      .card-bottom {
        padding: 8px;
        line-height: 1.5;
      }

      .card-title {
        font-weight: bold;
      }

      core-header-panel {
        width: 100%;
        height: 100%;
      }

      core-toolbar {
        color: #fff;
        background-color: #009688;
      }

Note: only when mode="cover" does this seem to fail, i.e. mode="tall" is fine.

If you remove the content from the second page's <section> it doesn't have any issues.

Also, this seems to be the most broken on chrome, firefox sort of obscures the bar it seems like, but I didn't test extensively.

I came across this issue because I had a centered <img> with about 200x200 dims which I wanted to cover the center of the toolbar on transition, but after transition, the toolbar would disappear. After some experimentation, seems to be for any content below the <core-toolbar>.

Polymer is awesome, keep up the good work!

googlearchive / core-animated-pages

hero-transition -> core-header-panel with mode="cover" fails #41