Undefined references are always due to failure to link to a library or object code module that contains the implementation of those classes or methods. I don't know about Debian, but on Windows you cannot link a debug mode program to release mode libraries or vice-versa. This could be another cause of undefined references.

Check your linker options to make sure you have included all of the necessary libraries or object files. If the undefined classes are QObject-based, make sure that MOC has been run to generate the moc*.cpp files and that these are also being compiled. Sometimes a qmake / make clean is needed.