The post-production (or pre-production, or filming) attribute only refers to the film's current status, not to your individual credit. In other words, it simply means that, to the best of our knowledge, the film is still in the post-production stage.
This is reflected by the way the credit is displayed. When the attribute is meant to indicate the film's current production status, it's listed immediately after the title and is displayed in red italics, like this:
Hulk, The (2003) (post-production) (technical supervisor)
If we want to indicate that someone worked as a post-production technical supervisor, their credit will instead appear like this:
Hulk, The (2003) (technical supervisor: post-production)
Note that the first type of attribute changes over time, while the second doesn't. In other words, as soon as the film is completed or released, the post-production attribute will disappear and won't be displayed next to the title anymore.