Please tell me what you think of this situation...

We are remodeling our kitchen. In June, our general contractor moved our dishwasher, but did not hook it up correctly and the water leaked into the ceiling of our basement and caused some significant damage. Our insurance covered all the damage and we paid Roto Rooter (about $500) to come out and "fix" things below the sink. This included rehooking up the dishwasher and running a new water line to our refrigerator. This was also with our old sink, faucet, and countertop. We weren't ready to install the new stuff yet.

In August, we had the sink and faucet pulled out with the old countertops. The day the new countertops were installed, I had a different plumbing company come out to hook up our new faucet and new sink. The old sink was a double bin sink and our new sink is a single bin, so the plumber needed to do some things below the sink with the pipes. I also asked him to rehook up the garbage disposal. He refused to hook up the garbage disposal because it was hard wired and said that was not safe. None of the other plumbers we've had out ever complained, so I didn't know it was a big deal, but I said okay, I'd have an electrician take care of that. So, he did a few things and we scheduled him to come out the following week after I had an electrician rewire the garbage disposal. A week later he comes out again to finish up his work. The electrician was a no-show (argh!) so when the plumber came out I told him not to worry about the garbage disposal and just to take care of everything else. He went ahead and did his thing below the sink and he did "install" the garbage disposal although it was not plugged in or anything. So, I pay him $500 or so. He leaves and that night I notice that when I run the faucet (he installed) in our new sink that the water drains into the dishwasher. If I hit "drain" on the dishwasher, the water drains out and everything is fine. But obviously this is a problem, if the water is draining into the dishwasher. I called the plumbing company for the third time to get them to come out and they tell me that since they did not hook up the dishwasher this was not their fault. I told them that the dishwasher was fine the problem was with the way their plumber installed the sink and faucet. This problem did not exist with the old sink and faucet and only started after he installed the new fixtures. After a 15 minute "conversation" w/them, I finally gave up and told them I would find someone else. The electrician who came to install the disposal actually used to be a plumber, so while he was there working on the electrical he took a look under our sink and adjusted with the hoses. I'm not sure exactly what he did, but I think he moved one hose, so it was up higher. It took him about 5 minutes and it appears to have solved the problem.

So, am I wrong to think that the plumbing company who installed the sink and faucet, should have fixed it so it didn't drain into the dishwasher? I'm not sure why he didn't check that before he left? Even if he didn't install the dishwasher, since he was coming in afterwards and installing everything else, isn't this something he should have checked? Why would I want to install a new faucet and sink to have it not work correctly?

Thanks in advance for your advice.