Mixing all three oscillator shapes gets lesser sound

[PlankTon]

Hello!

I am writing here because I suspect something is wrong with my MiniBrute. I have compared it with SH101 and with one another MiniBrute and they both act differently than mine. The problem is when I raise the mixer sliders of different oscillator shapes I would suspect I should get "more fatter" sound. But in my case I get thinner sound as if one shape would be a bit out of phase with the other. I don't know the exact design of the oscillator and maybe something like this is even theoretically impossible, but this is what I hear. I have tried this with another MiniBrute an there this didn't happen and it was even more different with Roland SH101. When I raised all three wave shape sliders there, the sound got richer.
Here is the video of my problem: https://dl.dropboxusercontent.com/u/10439245/Brute%20Summing.mp4

Is this kind of behavior normal?

Thanks.