Oh god, it was a "syntax error" again.
It works if I list the 1080i29 alone. madVR reports 59.940Hz and the TV does the deinterlacing.
I wonder why 1080i50 triggers the interlaced 50Hz and 1080i29 the interlaced 59.94Hz
It's not only testing. I would actually watch some episodes from a TV Show tonight.