I agree that the end result is that the POST data is formatted differently and the difference in header value is more a consequence of that and a sympton rather than a cause. One thing I didn’t mention explicitly is that I’ve never known PHP to behave like .NET does in this situation, so the behavior came as somewhat of a surprise to me.

I’m the main author of libcurl, and while I’m not fluent in PHP nor in the curl extension for PHP, I must say that your post/explanation here greatly misses the point. The problem is really _not_ the Content-Type: header. Most likely servers don’t care one yota about that header.

What counts, is that you made a multipart formpost instead of a regular one. The entire POST was done in a completely different encoding as url-encoding and multipart are far far away from each other.

(Me personally, I don’t like how the curl exension made the two different posts that easy to mix up.)

Have fun with that scraping!