[TYPO3-mvc] Dispatch Error after adding Boolean Property to Demand Class

[g4-lisz at tonarchiv.ch]

He there

In my searchform demand class i added a new property "isLocalKanton":

         /*
          * Local to Kanton
          *
          * @var boolean $isLocalKanton
          */
         protected $isLocalKanton = false;

         /**
          * @param  boolean $isLocalKanton
          * @return void
          */
         public function setIsLocalKanton($isLocalKanton) {
                 $this->isLocalKanton = (boolean)$isLocalKanton;
         }

         /**
          * @return boolean isLocalKanton
          */
         public function getIsLocalKanton() {
                 return $this->isLocalKanton;
         }

In the view i added a checkbox to the form:

<f:form name="demand" pluginName="fe_search_results" object="{demand}" 
action="results" pageUid="26">
<f:form.checkbox property="isLocalKanton" value="1" />
     [...]
</f:form>

Before this change, everything worked flawlessly.

Now i get the error: "Could not ultimately dispatch the request after 
101 iterations. Most probably, a @dontvalidate annotation is missing on 
re-displaying a form with validation errors."

Why is this? I can't see any mistake in my code...

Any help will be much appreciated!
Cheers, Till