Nested polymer templates select issue

Question

Settings: Using Polymer 1.0. Inside a dom-repeat there is a select tag and inside this, there are a couple of options, which i want to list from an array.

The issue: It's working perfectly fine on Chrome based browsers, but in IE, Safari or Firefox (See my issue here: https://i.stack.imgur.com/HKYNP.png ) there is nothing inside the second template, not a single option.

Source: Using this code for it:

<template>
    <ul>
        <template is="dom-repeat" items="{{actionattributes}}" as="actionattribute" index-as="attributeIndex">
            <li>
                <label>
                    ...
                </label>
                <label class="type-container">
                    <em>Type:</em>
                    <select name="{{generateActionFieldName(attributeIndex, 'type')}}" disabled="{{actionattribute.factory}}">
                        <template is="dom-repeat" items="[[type_list]]" as="attributeType">
                            <option value="{{attributeType}}" selected="{{isSelectedAttribute(attributeType, actionattribute)}}">{{attributeType}}</option>
                        </template>
                    </select>
                </label>
                <label >
                    ...
                </label>
                <button>
                    ...
                </button>
            </li>
        </template>
    </ul>
</template>

Any help appreciated!