QT Debugging symbols

Hi,

I try to debug a Qt problem for which I need debugging symbols. According to this howto I should use an override.
I added a optional override in shell.nix.
It starts to compile a qt and drops into a shell, but the resulting binary is still linked to a stripped version of qt.
What do I do wrong ?

Please check my current attempt at `plasmashell -v` segfaults · Issue #220168 · NixOS/nixpkgs · GitHub