Using Cubase 7.5

My piece has time signature 12/8. That is, I expect to find a measure divided by 4, and in each division I expect to find 3 sub-divisions. I set the Time Signature to 12/8 from measure 9. But I get this (see attached).

As you will see, the measure is divided into 6! Not 4. And the sub-divisions are 3. So in a measure I get 18, and not 12.

Needless to say this causes havoc with the timing (and when I export as MusicXML) when I quantize to 1/8T! (see attached).

Question: how can I set time signature to 12/8 correctly?

Thanks.