self-compiled wwWidgets 4 (msvc 2013 32-bit) prevents designer from starting up

I'm trying to integrate wwWidgets for Qt5, using msvc 2013 under Windows 10. It compiles and installs, but afterwards I'm not able to start designer any more.
This is what I do:
1) start a Qt for MSVC 2013 shell (32 bit)
2) vcvarsall.bat x86
3) cd <directory_where wwwidgets_source_resides>
4) qmake wwwidgets4.pro
5) nmake
6) nmake install

now trouble begins: designer refuses to start.

7) nmake uninstall

designer starts again.

Am I doing something wrong?

Kind regards,

Michael Bergmann