It seems like this line in tests/auto/api/tst_api.cpp causes it:
setupParams.setPluginPaths(prefs.pluginPaths(qbsRootPath + QLatin1String("/lib")));

Would be cool if the already available variable QBS_LIBRARY_DIRNAME qmake variable would affect this.

Setting the pluginsPath setting is no viable workaround here since if i set that to the same folder it fails for 32bit builds (it then finds the plugins two times and fails due to that (but it then works for 64bit)

Basically hardcoding to "lib/" is always wrong on linux.

Regards,
Erik