Damn, you are right... My problem is that I want first to set the text with the normal "Set text" action in order to get its height in pixels and create a speech balloon that will dynamically encapsulate it. A dt after that, I was clearing the text and added the "Type text" with the function call.
On closer inspection, it seems like I can't have any "Set text" type of action before the "Type text" action if I want to use a function call. However, if I use the function call with the normal "Set text" action and then add the "Type text" action and set it to type the text that was set above, it does work!
Check this example! It demonstrates what I am trying to say above http://www.eli0s.com/Tests/TypeTextFunc ... ample.capx
(for some reason you have to use "Save Link As", else it opens a tab with mashed text