All the people saying it is a copyright violation are in fact wrong.

Copyright protects a specific expression of an idea or group of ideas. It does not address the use of a copyrighted work as a template for generating other copyrighted works that use alternate expressions.

If you create a copyrighted work that consists of the phrase "The rain in Spain falls mostly on the plain." and someone comes along and very carefully creates a work of parallel intent that includes the phrase "In Spain, precipitation occurs mostly on the lowland prairies."; they are NOT violating your copyright. What they are doing may be sleazy, dishonest and lazy, but it isn't legally actionable.

This is actually a fairly deep topic, our legal system is constrained to working with tangible expressions and cannot identify the similarity between two expressions of an idea that share the same semantic structure (meaning) and yet have completely different linguistic surface (text).

Now if you can show that their works were mechanically derived from yours, that may be a different kettle of fish.

Really? So how do you align that with e.g.http://en.wikipedia.org/wiki/Derivative_work or the 'without prejudice' clause in art. 2.3 of the Berne Convention?

A mere claim that something is a deriviative work doesn't make it so; you'd have to show priority, connection and derivation. All of which are trickier than you'd think. If a company sends out a press release and two bloggers write stories about that company that are substantively similar but not word for word identical and one of them accused the other of copying, that would be a difficult case to prove.

Generally speaking a derivative work implies the overt appropriation of elements of the original; for instance if you write a novel about the rich inner life of Ernst Stavro Blofeld, that would be derivative of Ian Fleming's body of work. If however, you write a novel about a spy with a sex addiction problem who works for the Dutch Secret service and is blond and you very carefully avoid duplicating any precise plot points from any of the James Bond novels, it may be derivative in the sense that it's obvious you were emulating Ian Fleming, but it would not legally be a derived work.

> A mere claim that something is a deriviative work doesn't make it so

Obviously. But there is no way to tell from the OP's story. The way the OP presented the facts, the interpretation is that it's a derivative work. Someone took his text and shuffled it around just enough to make it not word for word identical. How the dice will roll in court is always tricky to say, and impossible in a case where you only have a general description of the facts, and only from one party at that.

The point is that a derivative work is protected just like the original. The evidence is a whole other matter, one that nobody, in this particular case, can judge from the information given.