If I run src/bluetooth/bluez/generate before building the build fails with:

{{make[3]: Entering directory '/home/lisandro/debian/pkg-kde/git/qt/qt5/qtconnectivity/qtconnectivity/src/bluetooth' }}
g++ -c -include .pch/Qt5Bluetooth -g -O2 -fdebug-prefix-map=/build/qtbase-opensource-src-vOmgd5/qtbase-opensource-src-5.10.1+dfsg=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_F
ORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/home/lisandro/debian/pkg-kde/git/qt/qt5/qtconnectivity/qtconnectivity=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -
{{std=c++1z -fvisibility=hidden -fvisibility-inlines-hidden -fno-exceptions -Wall -W -Wvla -Wdate-time -Wshift-overflow=2 -Wduplicated-cond -Wno-stringop-overflow -D_REENTRANT -fPIC -DCONFIG_LINUX_CRYPTO_API }}
-DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT -DQT_BUILD_BLUETOOTH_LIB -DQT_BUILDING_QT -DQT_NO_CAST_TO_ASCII -DQT_ASCII_CAST_WARNINGS -DQT_MOC_COMPAT -DQT_USE_QSTRINGBUILDER -DQT_DEPRECATED_WARNINGS -DQT_DISABL
E_DEPRECATED_BEFORE=0x050000 -DQT_NO_EXCEPTIONS -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -DQT_NO_DEBUG -DQT_CORE_LIB -DQT_CONCURRENT_LIB -DQT_DBUS_LIB -DQT_CORE_LIB -I. -I../../include -I../../include/QtBl
uetooth -I../../include/QtBluetooth/5.10.1 -I../../include/QtBluetooth/5.10.1/QtBluetooth -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore/5.10.1 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore/5.10.1/Qt
Core -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/include/x86_64-linux-gnu/qt5/QtConcurrent -isystem /usr/include/x86_64-linux-gnu/qt5/QtDBus -I
{{.moc -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -o .obj/objectmanager.o bluez/objectmanager.cpp }}
{{In file included from bluez/objectmanager.cpp:12:0: }}
{{bluez/objectmanager_p.h:39:30: error: 'ManagedObjectList' was not declared in this scope }}
{{     inline QDBusPendingReply<ManagedObjectList> GetManagedObjects() }}
{{                              ^~~~~~~~~~~~~~~~~ }}
{{bluez/objectmanager_p.h:39:30: note: suggested alternative: 'QObjectList' }}
{{     inline QDBusPendingReply<ManagedObjectList> GetManagedObjects() }}
{{                              ^~~~~~~~~~~~~~~~~ }}
{{                              QObjectList }}
{{bluez/objectmanager_p.h:39:47: error: template argument 1 is invalid }}
{{     inline QDBusPendingReply<ManagedObjectList> GetManagedObjects() }}
{{                                               ^ }}
{{bluez/objectmanager_p.h:46:62: error: 'InterfaceList' has not been declared }}
{{     void InterfacesAdded(const QDBusObjectPath &object_path, InterfaceList interfaces_and_properties); }}
{{                                                              ^~~~~~~~~~~~~ }}
{{bluez/objectmanager_p.h: In member function 'int OrgFreedesktopDBusObjectManagerInterface::GetManagedObjects()': }}
{{bluez/objectmanager_p.h:42:91: error: cannot convert 'QDBusPendingCall' to 'int' in return }}
{{         return asyncCallWithArgumentList(QStringLiteral("GetManagedObjects"), argumentList); }}
{{                                                                                           ^ }}
{{make[3]: *** [Makefile:1990: .obj/objectmanager.o] Error 1 }}
{{make[3]: Leaving directory '/home/lisandro/debian/pkg-kde/git/qt/qt5/qtconnectivity/qtconnectivity/src/bluetooth' }}
{{make[2]: *** [Makefile:48: sub-bluetooth-make_first] Error 2 }}
make[2]: *** Waiting for unfinished jobs....

As the source files are all part of the tarball this is definitely a bug.

By the way this files should be really created at build time. qdbusxml2cpp should be already present at build time so there is no really reason not to do it.