Broken Dropout - New Bike

Evening folks,

So, I'll start at the beginning. Yesterday I bought a bike(I won't say where, pending a phone call to the shop). Because the majority of the stock was boxed, it would take a day or so before the bike would be ready, so I opted to assemble it at home and save myself another trip.

The assembly consisted of attaching the handlebars, aligning them, installing the front wheel only, mounting the pedals and inserting the saddle. All easy stuff which I know I'm well capable of doing, and have done dozens of times before on my own bike.

Afterwards, I did all the usual checks and made sure that everything was tight, and cycled through the gears and did a quick brake test outside the house. All good. This evening I took the bike out for a quick spin to see how it felt on a longer cycle. About 2km up the road, and just before a steep enough descent I decided to give the brakes another go since I had only really been climbing so far.

Doing maybe 15-20kph I tested how the front felt - fine. Back up to 15-20kph and tried the back. Almost straight away the thing starts to skid. Let off a bit of pressure and I'm still skidding. I stopped on the road using the front brake. Couldn't figure out for a second what was wrong until I got off and had a look.

The rear dropout on the left hand side of the bike had given way, and the wheel was totally out of place. I'd say if I had been going and faster, the wheel would have come completely out of place on the left hand side, meaning that the right side would also have come out, leaving me with no rear wheel at all!

Comparing the design of the drop out to my Trek, I believe it to be a design flaw, as there is very little material in the area where maximum stress would occur during braking. This should never have happened no matter how hard I braked. (Honestly though, I wasn't being anywhere near as hard on it as I've been to my own bike because I'm not used to disks.)

My next step is to go back to the shop and see what they say about it. I know that the frame is pretty much beyond repair, but I don't want a replacement either. I don't want to discover a new frame has succumbed to the same flaw at 50kph in traffic. Even if a replacement never brakes, I've lost all confidence I had in the brand. I'm not looking for compensation for what might have been, I just want a full refund. Do you think that this is a reasonable request?

I have attached pictures of the broken dropout too, so you can see what I'm on about.

Regards,
Kevin.