Can't delete an empty item-set occurrence

[alansemenov]

1. Create a part that uses the descriptor shown below.
2. Add the part to a page and add a few occurrences (the amount doesn’t seem to matter) with text in each field.
3. In one of the added occurrences, delete values in all of the text fields.
4. Click “Apply”
5. Refresh the page.
6. Attempt to delete the item with the empty text fields
7. Click “Mark as ready”
8. The item re-appears.

<part xmlns="urn:enonic:xp:model:1.0">
    <display-name>Trekkspill</display-name>
    <form>
        <item-set name="accordion">
            <label>Trekkspill</label>
            <occurrences minimum="2" maximum="0"/>
            <items>
                <input name="title" type="TextLine">
                    <label>Tittel</label>
                    <occurrences minimum="1" maximum="1"/>
                </input>
                <input name="anchorId" type="TextLine">
                    <label>Ankerid</label>
                    <help-text>Setter inn anker-id som kan legges til etter selve url'en.</help-text>
                    <occurrences minimum="0" maximum="1"/>
                </input>
                <input name="html" type="HtmlArea">
                    <label>Innhold</label>
                    <occurrences minimum="1" maximum="1"/>
                </input>
            </items>
        </item-set>
    </form>
</part>