Issues with image in content using a shortcode


I am writing a call to action shortcode. The idea is to allow the user to add a title, description and button, which will open a modal.

The parameter for the modal content is:

'modal_content' => '',

Now if I create my shortcode [calltoaction modal_content="my content"], it works fine. In fact, if I add a whole lot of text it works just fine.

However, here is the issue, if I add a image to in between the text, then it shows nothing. So, somehow I does allow me to add normal text but it does not work / show anything any longer if I add an image to the content that is supposed to show in the modal.

Any great advice?