It might be the cistern water level is too low. High enough to expell the waste but not to replenish the water trap to normal level.
Adjust the water level in cistern so its higher, but not too high it starts running into the internal overflow especially if you are on a water meter, so more will flush through, you may find this wil cure the lack of water in the bowl, obviously needed to prevent smells from sewer drifting back.
BB, February 2012
