The toilet in my house on the second floor flushes strange. It's a new construction house so the toilet is brand new. When I trip the lever, the water seems to go into the bowl slow, like things are happening in slow motion.

When it flushes, the bowl fills and the water level rises a little as normal, then the water in the bowl goes down for just a split second and then comes back up quickly. Therefore, whatever contents (i.e. toilet paper) that doesn't catch the jet of water from the siphon jet remains in the bowl.

The toilet is a 1.6 gal. American Standard elongated bowl with ball and flapper. I've plunged the toliet, adjusted the water level in the tank, checked the holes in the rim to no avail. Does the way the sewer pipe is routed have any effect? I think it goes down from the wax ring about 5 inches and then makes a 90 degree elbow turn to a horizontal pipe.

I have the same model toilet in two other bathrooms in the house and they flush good. Anyone know what's going on? Thanks.