TYPO3.Fluid

I have a M:N relation between my two model "book" and "category".

Now I try to create a multiple select with the SelectViewHelper like that:

<f:form.select property="categories" options="{categories}" optionLabelField="name" multiple="multiple" size="7" />

{categories} is a variable assigned in the controller.
that works fine, all, categories are shown in the select.

The problem is, that none of my preselected categories are selected.

The html output looks like that:

<input type="hidden" name="book[categories]" value="" />
<select id="categories" multiple="multiple" size="7" name="book[categories][]">
<option value="0bc305ec-8aff-4fa8-bdeb-476d7c21c841">Novels</option>
<option value="8c2221e3-a3fd-4ce2-8f7e-66aac9eed5f5">Second Category</option>
<option value="c1ca0c2d-08c4-4b22-b9c7-69bbd42de840">Third category</option>
</select>

I analized the problem and it seems, that the method "getSelectedValue" in the "SelectViewHelper" can't handle multiple preselects.

I think the problem is also in the blog-tutorial when you try to edit post which already has related posts, they are not selected.