Computing a stringhash on QObject property lookup can cause V8 to assert

In some cases, v8 will assert during creation of a QHashedV8String:

import QtQuick 2.0

Item {
    id: root
    width: 300
    height: 300
    property string propName: width
    function slotA () {
        height = width;
    }
    Component.onCompleted: root[propName + "Changed"].connect(slotA);
}

The result of the concatenation is placed on the stack, the QV8QObjectWrapper's Getter interceptor is entered, and a QHashedV8String is constructed from the property (name). During construction, v8 asserts:

#5 0xb5c2f9b2 in CheckHelper (file=0xb5ff65b0 "../3rdparty/v8/src/objects-inl.h", line=2050, source=0xb5ff685e "object->IsSmi()",
condition=false) at ../3rdparty/v8/src/checks.h:60
#6 0xb5c33af2 in v8::internal::Smi::cast (object=0xdeadbeef) at ../3rdparty/v8/src/objects-inl.h:2050
#7 0xb5c5b832 in v8::internal::SeqString::symbol_id (this=0x2c7c0fc5) at ../3rdparty/v8/src/objects-inl.h:2102
#8 0xb5c4bcab in v8::String::CompleteHash (this=0x80f3930) at ../3rdparty/v8/src/api.cc:3734
#9 0xb6b938b6 in QHashedV8String (this=0xbfffb998, string=...)
at ../../include/QtDeclarative/5.0.0/QtDeclarative/private/../../../../../src/declarative/qml/ftw/qhashedstring_p.h:876
#10 0xb6cef76f in QV8QObjectWrapper::Getter (property=..., info=...) at qml/v8/qv8qobjectwrapper.cpp:702

Which suggests either that the string has wrongly been tagged as a SeqString or that the memory for the symbol_id was not allocated correctly.

/edit: some more test cases to illuminate the cause of the problem:

// works fine
import QtQuick 2.0
Item {
    id: root
    width: 300
    height: 300
    property int someRandom: 50
    Component.onCompleted: {
        console.log(root["some" + "Random"]);
    }
}

// produces undefined (as expected) but doesn't crash
import QtQuick 2.0
Item {
    id: root
    width: 300
    height: 300
    property int someRandom: 50
    Component.onCompleted: {
        console.log(root["somerandom"]);
    }
}

// crashes
import QtQuick 2.0
Item {
    id: root
    width: 300
    height: 300
    property int someRandom: 50
    Component.onCompleted: {
        console.log(root["some" + "random"]);
    }
}