Qt 5.14.0 MT, Access Violation, Qvarint::toString() -> QString::toStdString()

// --- qtbase/mkspecs/common/msvc-desktop.conf    2019-01-28 16:11:52.000000000 +0200
+++ qtbase/mkspecs/common/msvc-desktop.conf    2019-12-17 11:59:22.870978600 +0200
@@ -30,23 +30,23 @@
 QMAKE_CFLAGS_OPTIMIZE_SIZE = -O1
 
 QMAKE_CC                = cl
 QMAKE_LEX               = flex
 QMAKE_LEXFLAGS          =
 QMAKE_YACC              = bison -y
 QMAKE_YACCFLAGS         = -d
 QMAKE_CFLAGS            = -nologo -Zc:wchar_t
 QMAKE_CFLAGS_WARN_ON    = -W3
 QMAKE_CFLAGS_WARN_OFF   = -W0
-QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE -MD
-QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += $$QMAKE_CFLAGS_OPTIMIZE -Zi -MD
-QMAKE_CFLAGS_DEBUG      = -Zi -MDd
+QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE -MT
+QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += $$QMAKE_CFLAGS_OPTIMIZE -Zi -MT
+QMAKE_CFLAGS_DEBUG      = -Zi -MTd
 QMAKE_CFLAGS_YACC       =
 QMAKE_CFLAGS_LTCG       = -GL
 
 contains(QMAKE_TARGET.arch, x86_64) {
     # SSE2 is mandatory on 64-bit mode, so skip the option. It triggers:
     # cl : Command line warning D9002 : ignoring unknown option '-arch:SSE2'
     QMAKE_CFLAGS_SSE2   =
 } else {
     QMAKE_CFLAGS_SSE2   = -arch:SSE2
 }

    {
        QSettings settings_app("TEST", "TEST");
        settings_app.setValue("ABC", "string");
    }
    {
        QSettings settings_app("TEST", "TEST");
        std::string s = settings_app.value("ABC", "def string").toString().toStdString(); <<-- Access Violation
    }