[Reg 5.11->5.12] QtQuickCompiler in release builds results in broken translations

In all my projects using Qt 5.12 the translation is broken for release builds if

CONFIG+=qtquickcompiler

just wanted to start a more complex testing of Qt 5.12 Beta 3 with some Beta Testers of my Apps.
all my tests from debug builds are looking good, then I tested release builds and found a showstopper:
my Apps normally are in english and translated into german - most of my customers are from germany
all is translated using Linguist
then I noticed that translation in 5.12 release builds is broken:
on german devices, some translations are not done (see attached screenshots)
this happens on Android, macOS, iOS,
exactly same project and translation files are working well on 5.11.2
doesn’t matter if QtC 4.7.1 or 4.7.2
clear build dir, clean project, lupdate / lrelease doesn’t help
all can be tested from my QtWS 2018 conference app at github but happens on all of my projects

workaround for now: disabling Qt Quick Compiler