TYPO3 Core

Using TYPO3 6.2.4 and EXT:form in an installation with no third party extension installed and very simple basic TS page object using FLUIDTEMPLATE the entire frontend output of a very simple form by EXT:form is broken. Instead of the desired markup it outputs a mixture of some wrapping divs and the original Typoscript configuring the form. The current version of css_styled_content static Typoscript is included in root template.
Example:
http://typo3.aemka.de/index.php?id=8
Output of EXT:form:

<div id="c1" class="csc-default"><h1 class="csc-firstHeader">Test</h1><form action="seite-1.html" id="mailform" name="mailform" enctype="multipart/form-data" method="post" onsubmit="return validateForm('mailform','','','','')"><div style="display:none;"><input type="hidden" name="locationData" value="8:tt_content:1" /></div><fieldset class="csc-mailform"><div class="csc-mailform-label">enctype = multipart/form-data</div><div class="csc-mailform-label">method = post</div><div class="csc-mailform-label">prefix = tx_form</div><div class="csc-mailform-label">confirmation =</div><div class="csc-mailform-label">postProcessor {</div><div class="csc-mailform-label">1 = mail</div><div class="csc-mailform-label">1 {</div><div class="csc-mailform-label">recipientEmail = info@aemka.de</div><div class="csc-mailform-label">senderEmail = info@aemka.de</div><div class="csc-mailform-label">subject = Test</div><div class="csc-mailform-label">}</div><div class="csc-mailform-label">}</div><div class="csc-mailform-label">10 = TEXTLINE</div><div class="csc-mailform-label">10 {</div><div class="csc-mailform-label">name = test</div><div class="csc-mailform-label">label {</div><div class="csc-mailform-label">value = Test</div><div class="csc-mailform-label">}</div><div class="csc-mailform-label">}</div><div class="csc-mailform-label">20 = SUBMIT</div><div class="csc-mailform-label">20 {</div><div class="csc-mailform-label">name = 3</div><div class="csc-mailform-label">value = Formular absenden</div><div class="csc-mailform-label">}</div></fieldset></form></div>