If you build MITK with Qt 5 the plugin generator and the project template tests fail during the configure step with the following error message:

CMake Error at CMakeExternals/MITK.cmake:212 (if):

if given arguments:

  "my_qmake_executable" "AND" "NOT" "my_qmake_executable" "STREQUAL"

Unknown arguments specified

Reason is most likely that the cmake variable MITK_QMAKE_EXECUTABLE does not exist but it is used as argument for the STREQUAL.
(The my_qmake_executable is set to the value QT_QMAKE_EXECUTABLE and is empty)

Looks like we have to migrate these projects to qt 5.