can't find executable when using qbs.installDir

To reproduce:

• Create a new project and choose "plain C++ application"
• Choose qbs build system
• edit qbs file and add this line to the group: qbs.installDir: "../bin"
• build and run

It fails to start the application because it search for it in a bad place, here is the error prompted by qtcreator:
"Executable C:\projects\build-qtcreatorbug-sf112-Desktop_Qt_5_7_1_MSVC2015_32bit2-Debug\qtc_Desktop__a1af886e-debug\install-root\rbug-sf112.exe does not exist."

The correct path is : "C:\projects\build-qtcreatorbug-sf112-Desktop_Qt_5_7_1_MSVC2015_32bit2-Debug\qtc_Desktop__a1af886e-debug\bin\qtcreatorbug-sf112.exe"

See also how strange it is that it shortened the executable name...

It works fine with qtcreator 4.1