[TYPO3-mvc] Strange problems: switchableControllerActions and link action

[Sören Kracker]

Hi list,
I've already developed a few extbase extension but I'm stucked on a new 
one now.
When clicking on a link that should lead to my showAction I always get 
the listAction again.
The link is correctly generated. Controllername, action and argument are 
set.
?tx_myext_pluginname%255Bobject%255D=1&tx_myext_pluginname%255Baction%255D=show&tx_myext_pluginname%255Bcontroller%255D=Controllername&cHash=14346c02646d6f0b093c1d82266be779

The controller has both functions for the actions (set to public).

My switchableControllerActions (shown and selected in backend):
<items>
<numIndex index="0">
<numIndex index="0">some title</numIndex>
<numIndex index="1">Controllername->list;Controllername->show</numIndex>
</numIndex>
</items>

My localconf:
Tx_Extbase_Utility_Extension::configurePlugin(
     $_EXTKEY,
     'Pluginname',
     array(
         'Controllername' => 'list, show',
     ),
     // non-cacheable actions
     array(
         'Controllername' => 'list, show',
     )
);

My link action:
<f:link.action action="show" arguments="{object : 
object}">{object.title}</f:link.action>

What am I missing?