Mm, that´s unusual. Try sprinkling a layer of vermiculite over the seeds when you´ve sown them, that will help retain moisture, prevent fluctuations in temperature, and allow light through. Put a clear propagator lid over the tray, or put it in a clear plastic bag to increase the humidity, but when they start to germinate, give them ventilation so as to minimise damping-off. The vermiculite will help prevent damping-off too.
Don´t sow them too close together, they need room, and it will make it easier to prick them out. Put them somewhere light, with a reasonably constant temperature, not too hot, not too cold.
Always keep the compost moist, but not soaking wet.