I have the same problem with my iPhone 5. It started last week when I found out that the phone is not charging when connected. So I take out the cable and found out that the pins on the connector cable was black and have a burnt smell. I leave the phone for several minutes and tried to connect it again. I found out that cable only work on one side.
So I took some pictures and went to Apple online support to request for a new cable. I got a new cable and the problem still persists. Now I know that the problem is with the connector on the phone. I went to the Apple online support and request for a repair. I sent them the phone and they said that they put the repair on hold.
I telephoned the support centre asking why they put the work on hold, and they told me that the repair is not covered because the problem might be caused by liquid damage. I was pretty sure that it wasn't liquid damage because I believe I take extra good care of the £529 phone. The operator asked me to ask my insurance company (which I don't have) in case they cover that accident. The operator also told me that the repair cost, £152+VAT is cheaper than usual £170++VAT. It was very disappointing.
Pretty sure it wasn't liquid damage, I telephoned the support centre again, and this time the operator told me that it is because of accident and they don't cover it. She couldn't explain exactly what is the problem and connected me with a senior operator. The senior operator told me that the engineers think that it might be cause by liquid damage. Then I told her that I have pictures of the burnt cable. She let me send those pictures and they'll contact me again by tomorrow. So I still don't know what is the conditon of my claim.
So as a conclusion... The engineers think that the damage might be caused by liquid damage, but the term 'might' does mean that it 'might not' caused by liquid damage too. I have read other discussions telling that they found out that their cable has some corrosion on the pins even though there have not been any contact with liquid.
https://discussions.apple.com/thread/4363224?start=0&tstart=0
https://discussions.apple.com/thread/4566785?start=0&tstart=0
It looks like that I'm not the only one with the problem. I think the lightning connector itself is prone to corrosion. So I think that it is a design flaw, and Apple should cover the repair cost. Now I can only wait.
