Custom enfold element tiny_mce

Hi,
We are working with custom made enfold elements for a long time. We often have problems with the tiny_mce field.
I created two tiny_mce fields in a custom element:

array(
                    'name' => __('Immer sichtbarer Text', 'avia_framework'),
                    'desc' => __('Enter some content for this textblock', 'avia_framework'),
                    'id' => 'visible_text',
                    'type' => 'tiny_mce',
                    'std' => __('', 'avia_framework'),
                    'tmpl_set_default' => false
                ),

                array(
                    'name' => __('Eingeklappter Text', 'avia_framework'),
                    'desc' => __('Enter some content for this textblock', 'avia_framework'),
                    'id' => 'hidden_text',
                    'type' => 'tiny_mce',
                    'std' => __('', 'avia_framework'),
                    'tmpl_set_default' => false
                ),

If I edit the content of one of the fields and add a bold text and save the page everything is fine in the frontend but in the backend in the visual view of the tiny_mce field the bold text isn’t visible any more but <strong>Text</strong> is visible as code. If I save again the frontend text is also wrong because I the the html tags. What’s the problem?

Here is the complete code for the element: https://pastebin.com/Ptn91vBU

All the best,
Patrick