6. As an exception to the Sections above, you may also combine or link a "work that uses the Library" with the Library to produce a work containing portions of the Library, and distribute that work under terms of your choice, provided that the terms permit modification of the work for the customer's own use and reverse engineering for debugging such modifications.
If i understand right, when i deploy a commercial (closed source) application, i need to add to my license file that the users are permitted to "reverse engineer" my software???

OMG, say me that's not rue xD

ps. i did not modify QT, and im using dynamic dlls
pps. if i use templates /inline function, is that a derivate work? or a work which uses the library (without containing any parts of the library)?