Demoscene Passivist wrote

As far as I can see u don't unbind the FBO. So thats an explanation why u do not see anything :) If u don't unbind the FBO and rebind the other textures again in the next frame, but using the same texture unit, mapping will fail with multiple textures.

Sounds u have to dive deeper into the "texture unit"/"texture id" stuff. Maybe this thread helps ...