Can't build user project with qmake with a Qt6 built with -qtlibinfix XX

I built Qt 6.1.0 beta1 using the following configure: 

configure -release -qtnamespace XXX -qtlibinfix XX -opensource -confirm-license -skip qt5compat -skip qtdoc -skip qtquick3d -skip qtquickcontrols2 -skip qtquicktimeline -skip qtshadertools -skip qtwayland

So far so good, the build completed successfully.

However when building my Qt application (via Qt Creator 4.14.1+a QMake .pro file), at some point during the build it fails with the following message:

NMAKE:-1: error: U1073: don't know how to make 'C:\Qt\Qt-6.1.0b1\lib\Qt6EntryPoint.lib'

When checking the lib folder, there is a lib file named Qt6EntryPointXX.lib, as expected with the configure -qtlibinfix XX option. But for some reason it is ignored when qmake is looking for the Qt6EntryPoint lib (maybe because this file didn't exist in Qt5 and was not fully set up to use qtlibinfix ?).