Water coming back into the dishwasher?
Many dishawshers will have a small amount of water left in the bottom of the cabinet after the cycle has run - but it shouldn't be much. One thing you should check is to make sure your drain line goes up into an air gap valve at the sink.
If you haven't installed an air gap you should at least take the drain line from the DW up into a high loop before it terminates in the disposal or drain line. A high loop means running it up to just under the countertop. This is especially important if it drains into the disposal. The high loop uses gravity to keeps waste from the disposal from backing up into the DW.