SUMMARY
Sometimes when moving a subfolder into another parent folder kmail will crash with this infinite recursion

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f58721c9477 in QBasicAtomicInteger<int>::load (this=0x1100fa20) at /usr/include/qt5/QtCore/qbasicatomic.h:103
103         T load() const Q_DECL_NOTHROW { return Ops::load(_q_value); }
[Current thread is 1 (Thread 0x7f58fbdb7980 (LWP 18221))]
#0  0x00007f58721c9477 in QBasicAtomicInteger<int>::load() const (this=0x1100fa20) at /usr/include/qt5/QtCore/qbasicatomic.h:103
#1  0x00007f58721c9052 in QtPrivate::RefCount::isShared() const (this=0x1100fa20) at /usr/include/qt5/QtCore/qrefcount.h:101
#2  0x00007f58721de70a in QList<MessageList::Core::MessageItem*>::append(MessageList::Core::MessageItem* const&) (this=0x7ffe02012b20, t=@0x7ffe018150c0: 0xe0bf540) at /usr/include/qt5/QtCore/qlist.h:581
#3  0x00007f58721dbdab in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xe0bf540, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:587
#4  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0x724a9a0, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#5  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xeddcb20, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#6  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xe0bf540, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#7  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0x724a9a0, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#8  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xeddcb20, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#9  0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xe0bf540, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#10 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0x724a9a0, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#11 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xeddcb20, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#12 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xe0bf540, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#13 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0x724a9a0, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#14 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xeddcb20, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594
#15 0x00007f58721dbe62 in MessageList::Core::MessageItem::subTreeToList(QList<MessageList::Core::MessageItem*>&) (this=0xe0bf540, list=...) at /data/kde/src/5/kde/pim/messagelib/messagelist/src/core/messageitem.cpp:594

etcc, etc