Hidden buttons

Hi friends,

I have a problem with buttons (Rockettheme) not shown in the composer.

In my first image you can see a custom HTML block with an image, some text and a rockettheme button. The button exists, the link behind it is working, but the button is not shown.
link: http://www.kruwt.nl/stockfotografie/stockbureaus/shutterstock

The HTML module is named: shutterstock-aanmelden-module
the code is
<p><img title="shutterstock logo" src="/ ... images/stockbureaus/logos/shutterstock-logo-1.jpg" alt="" /></p>
<p>Bekijk mijn foto's op Shutterstock</p>
<p><a class="button button-2" href="/..." target="_blank">Bekijk foto's</a></p>
and the module is placed in the text by ".loadposition shutterstock-bekijk-positie."

I have tested the same custom HTML module in a 'normal' Joomla article. See http://www.kruwt.nl/testqqq
In that case, the buttons are shown as expected. (example second image)

So, what is happening with the buttons in the composer environment ??

Thanks for your answer,
Kind regards, T.W. van Urk