additional modes in waveport propagation

I'm trying to simulate a waveguide filter that has quite a large BW. I know from the simulating frequency that the second TE mode can propagate. However, when I add a second mode to the waveports I still get the following warning:

[info] Discrete solution, process hf3d: Port 2 (or 1) supports an additional propagating and/or slowly decaying mode whose attenuation is 1.960e-001 and propagation constant is 2.947e+002 (1:16:37 PM Feb 19, 2016)

Why do I still get this message even if I've told the waveport that there are two modes that should be propagated?