what's odd about this one

They go so out of the way to try to make us sympathize with the Sawyers, showing them as wronged, persecuted against, and so on, and that Leatherface is misunderstood. And him being honorbound to protect Heather, it's sort of implied it's a big misunderstanding, and that had she only read the letter earlier, she'd have been able to prevent him from killing so much. Then, beyond that, of the four young travelers killed, we're shown one is stealing from her, two are being unfaithful to her, and the other she just wasn't all that close with seemingly.

Additionally, Heather's adoptive parents. Okay, the way they got her wasn't the best. But it's common enough for parents to not tell adopted children as such, especially taking into account this particular history. When Heather learned the truth and confronted them, they didn't handle it terribly well, but who would. And knowing what they know, who could blame them for telling her not to go to Texas? Maybe they weren't the greatest parents, but they seemed to care, it's not like they were holding her for ransom.