JS `delete` operator leads to segfaults on garbage collecton or leaks memory rapidly

import QtQuick 2.0

Item {
  property var foo
  Component.onCompleted: {
    foo = {"key1":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key2":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key3":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key4":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key5":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key6":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key7":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"}
    var keys = Object.keys(foo)
    for (var i = 0; i < keys.length; i++)
      delete foo[keys[i]]

    gc() // Direct call not required, it also fails on subsequent automatic gc
  }
}

import QtQuick 2.0

Item {
  property var foo
  Component.onCompleted: {
    foo = {"key1":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key2":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key3":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key4":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key5":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key6":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
           "key7":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"}
    var keys = Object.keys(foo)
    for (var i = 0; i < keys.length; i++)
      delete foo[keys[i]]

    // Alternative to manual gc call — just do some stuff, it also crashes
    var x;
    for (var j = 0; j < 1000; j++)
      x = Array(200).join('0')
  }
}

#0  0x0000000000000000 in ?? ()
#1  0x00007f51412c0da7 in QV4::MemoryManager::mark() () from /usr/lib/libQt5Qml.so.5
#2  0x00007f51412c13ec in ?? () from /usr/lib/libQt5Qml.so.5
#3  0x00007f51414faab0 in QV4::GlobalExtensions::method_gc(QV4::BuiltinFunction const*, QV4::Scope&, QV4::CallData*) () from /usr/lib/libQt5Qml.so.5
#4  0x00007f514143e3e3 in QV4::Runtime::method_callActivationProperty(QV4::ExecutionEngine*, int, QV4::CallData*) () from /usr/lib/libQt5Qml.so.5
#5  0x00007f5141eaeab4 in ?? ()
#6  0x0000000000000000 in ?? ()

#0  0x0000000000000000 in ?? ()
#1  0x00007ff183925da7 in QV4::MemoryManager::mark() () from /usr/lib/libQt5Qml.so.5
#2  0x00007ff1839263ec in ?? () from /usr/lib/libQt5Qml.so.5
#3  0x00007ff183927ff8 in QV4::MemoryManager::allocString(unsigned long) () from /usr/lib/libQt5Qml.so.5
#4  0x00007ff183a0547a in QV4::ExecutionEngine::newString(QString const&) () from /usr/lib/libQt5Qml.so.5
#5  0x00007ff183a23684 in ?? () from /usr/lib/libQt5Qml.so.5
#6  0x00007ff183aa726a in QV4::Runtime::method_callProperty(QV4::ExecutionEngine*, int, QV4::CallData*) () from /usr/lib/libQt5Qml.so.5
#7  0x00007ff184512ba4 in ?? ()
#8  0x0000000000000000 in ?? ()