Version:           unspecified (using Devel) 
OS:                Linux

I ran gdb, interrupted and did a backtrace:

MessageList::Core::Item::parent (this=0x24f52f0) at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/item.cpp:408
408     /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/item.cpp: File o directory non esistente.
        in /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/item.cpp
(gdb) bt
#0  MessageList::Core::Item::parent (this=0x24f52f0) at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/item.cpp:408
#1  0x00007fff9876899d in MessageList::Core::MessageItem::topmostMessage (this=<optimized out>)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/messageitem.cpp:596
#2  0x00007fff98773ac0 in MessageList::Core::ModelPrivate::viewItemJobStepInternalForJobPass1Fill (this=0xc0c170, job=0x1d479c0, tStart=...)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:2933
#3  0x00007fff9877589d in MessageList::Core::ModelPrivate::viewItemJobStepInternalForJob (this=0xc0c170, job=0x1d479c0, tStart=...)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3385
#4  0x00007fff98775ece in MessageList::Core::ModelPrivate::viewItemJobStepInternal (this=0xc0c170)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3772
#5  0x00007fff98776988 in MessageList::Core::ModelPrivate::viewItemJobStep (this=0xc0c170)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3988
#6  0x00007fff987786e6 in MessageList::Core::Model::qt_metacall (this=0xc06300, _c=QMetaObject::InvokeMetaMethod, _id=<optimized out>, _a=0x7fffffffd510)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/model.moc:90
#7  0x00007ffff5c79f0a in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#8  0x00007ffff5c7d7d9 in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#9  0x00007ffff663cd94 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#10 0x00007ffff6641c01 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#11 0x00007ffff7347e26 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#12 0x00007ffff5c672fc in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#13 0x00007ffff5c93da2 in ?? () from /usr/lib/libQtCore.so.4
#14 0x00007ffff5c91554 in ?? () from /usr/lib/libQtCore.so.4
#15 0x00007fffef4dd6d3 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0


continued... then did the same

0x00007fff98768990 in MessageList::Core::MessageItem::topmostMessage (this=<optimized out>)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/messageitem.cpp:595
595     in /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/messageitem.cpp
(gdb) bt
#0  0x00007fff98768990 in MessageList::Core::MessageItem::topmostMessage (this=<optimized out>)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/messageitem.cpp:595
#1  0x00007fff98773ac0 in MessageList::Core::ModelPrivate::viewItemJobStepInternalForJobPass1Fill (this=0xc0c170, job=0x1d479c0, tStart=...)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:2933
#2  0x00007fff9877589d in MessageList::Core::ModelPrivate::viewItemJobStepInternalForJob (this=0xc0c170, job=0x1d479c0, tStart=...)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3385
#3  0x00007fff98775ece in MessageList::Core::ModelPrivate::viewItemJobStepInternal (this=0xc0c170)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3772
#4  0x00007fff98776988 in MessageList::Core::ModelPrivate::viewItemJobStep (this=0xc0c170)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/core/model.cpp:3988
#5  0x00007fff987786e6 in MessageList::Core::Model::qt_metacall (this=0xc06300, _c=QMetaObject::InvokeMetaMethod, _id=<optimized out>, _a=0x7fffffffd510)
    at /chakra/desktop-unstable/kdepim/src/kdepim-4.7.90/messagelist/model.moc:90
#6  0x00007ffff5c79f0a in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#7  0x00007ffff5c7d7d9 in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#8  0x00007ffff663cd94 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#9  0x00007ffff6641c01 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#10 0x00007ffff7347e26 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#11 0x00007ffff5c672fc in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#12 0x00007ffff5c93da2 in ?? () from /usr/lib/libQtCore.so.4
#13 0x00007ffff5c91554 in ?? () from /usr/lib/libQtCore.so.4
#14 0x00007fffef4dd6d3 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#15 0x00007fffef4ddeb0 in ?? () from /usr/lib/libglib-2.0.so.0

All this time CPU is at 100% and UI is not responding.

Reproducible: Always

Steps to Reproduce:
Open kmail2 or kontact

Actual Results:  
lockup

Expected Results:  
no lockup

kdepim 4.8 beta2 on chakra linux