DJM 900 Nexus, Mic 2 input unbalanced

I have had all kind of troubles with the mic 2 input on the rear side of the mixer. There was lot's of hum when I connected a microfone. I used a balanced microfone cable. I tried a lot of other balanced cables, an the problem was the same. First I thought there was a problem with the mic 2 input.

Then I tried to use an unbalanced cable, and now it works fine. So my question is, if it's normal on quality mixers, that the microfone input is unbalanced when the mixer is mounted with a jack input.

And It could have been great, if Pioneer have mentioned in the mixers specifications, that the mic 2 was unbalanced. Then I could have avoided all my problems from the very beginning.