It says it is "derived from" and "inspired by" it. But it also says "Our libraries can be linked directly into any standard C++ application" which the LGPL of Qt 4 disallows (unless your application is open source, but then that isn't any application).

Copperspice is LGPL. Like Qt, it can be dynamically linked into any standard C++ application. The key is that the user needs to be able to instead use their own version of Qt/CS, if they want.