qt5_generate_repc() outputtype string compare fails

In order to generate rep_MyObject_source.h header file I call the qt5_generate_repc() macro like this:

qt5_generate_repc(MYSRCS MyObject.rep SOURCE)

But the macro always generates replica header files because in Qt5RemoteObjectsMacros.cmake the Line 64 does never evaluate to true

if(${outputtype} STREQUAL "SOURCE")

To reproduce the problem i set up a small script. I couldn't find any value for REPC_TYPE which makes the last if() evaluate to true.

set(REPC_TYPE "SOURCE")
if("${REPC_TYPE}" STREQUAL "SOURCE")
    message("this works")
endif()
if(${REPC_TYPE} STREQUAL SOURCE)
    message("this works too")
endif()
if(REPC_TYPE STREQUAL "SOURCE")
    message("and this works too")
endif()
if(${REPC_TYPE} STREQUAL "SOURCE")
    message("but this, nooo, never")
endif()

Resetting CMakeCache and rerunning cmake did not solve the problem.