Where you live can 'affect' the vinyl. FOr example, if you live in the SE or SW, vinyl isn't a good deal because of the extremes in temp. This is not to say that the NE and NW USA don't have extremes but the weather in the SE and SW seems to affect vinyl more. It's my understanding that it's not that popular down there.
Anyways, the installation has an affect too. If the nail-heads are hammered right to the sheathing, then the vinyl WON'T be able to expand. If this is the case, the vinyl should be re-nailed with the heads slightly off of the sheet. It is NOT appropriate to simply pull out the nail a little! In doing this, the sheet is not 'loose'.
As you stated, another reason the vinyl bends and warps is because of the underlying sheathing. It can be 'unevenly' installed. OR, if the vinyl is a dark color (which absorbes heat more than light colors), and the underlying sheathing has a 'foil-face', the heat can build up under there and get reflected 'outwards', thus, warping the vinyl.
The question is, what to do. Well, whenever you make a call to your builder to 'report' a problem, back it up with a certified mail, return-receipt letter as well. In the letter, you state your problem and ask him to fix it. You also say you will be following up your letter with a phone call (even though you already did that.) The FIRST and every following contact (either by phone, letter, or in person) you have with your builder or any of his 'contractors', you document. In this notbook, you date it, get names, state the problem, state the reason for making the note, and summarize the 'encounter' / 'meeting' / 'whatever'. IF, for some reason, you have to go to court, the judge is going to want to see proof of your phone calls, visits to the builder, meetings with his contractors, 'fixes', and so on. You should take pictures too BEFORE the fix and AFTER the fix. I'm sure it's possible that the 'fix' will go bad in time too. Take pictures from many angles. DON'T skimp on the film or development costs! You'll need all the 'ammunition' you can get if you go to court!
Start your notebook now where the first entry is you noticing the problem. THe next entry is when you called him. THe next entry is when he called you. And so on. Since you probably don't have pictures of the first fix, take whatever pictures you can now of him making the fix and the OTHER problems w/the house. If you have to, 'number' your pictures by taping a piece of paper to the wall or whatever, and making a note in your notebook of what picture #4 is, and so on. This way, you don't have to try to remember what you were taking a picture of when you took it. Chances are months may go by until you get the film developed!
As long as the builder is making the 'fixes', he IS making 'reasonable' attempts to make the fix. (DO note the dates and related info of the fix in your book.) The judge would say that he is doing what he should be doing - IE., making a reasonable attempt to fix the problem. If he refuses to make other fixes, again, you should have pictures, make a note in your book about your 'conversation', and follow it up with at certified, return-receipt letter! CYA if you know what I mean.
If you need more info, e-mail me. My best to ya and hope this helps.