Special blocks for `.docx` export

I am desperately trying to get special blocks to export to `.docx`, but it won't work. At first I thought I was missing the right backend, but then I came to realize the problem lays deeper. Even defining this custom block did not yield any result:

``` lisp
(org-defblock satz nil (name "" label "") "Custom block for the custom satz-environment in LaTeX."
(print "hello!"))
```
For all `.tex` and `.html`, it is replaced by "hello!" every time.

It seems to me that something is converting the block _before_ the formatting function of `org-special-blocks-extra` comes into play. What could the reason for that be, and what could you do about it?