What image did you use? Could you give us the file on which the bug happens?

The image is 1.4MB so I cant upload here.

My system is pretty good (2.4GHz dual core, 3GB RAM, Nv 9300M) so its not hardware.

I reinstalled Krita (same version) and now cant replicate problem, but it was consistent before.  However, the process that caused the problem was:

Start with CMYK template,
Add image,
duplicate image,
Apply adjust levels to duplicated image.

The apply levels part seemed to be when the problem started.  I often have Krita accidentally close itself when you hit "apply and close" on the levels adjustment.  But it does not happen all the time unfortunately.

I even get a crash on duplicate: 


Thread 1 (Thread 0xb388e920 (LWP 483)):
[KCrash Handler]
#6  QBasicAtomicInt::ref (this=0x21) at /usr/include/QtCore/qatomic_i386.h:120
#7  0xb71689b2 in KisSharedPtr<KisSharedData>::attach (this=0x8765894, p=0x1d) at /home/boud/kde/src/koffice/krita/image/kis_shared_ptr.h:397
#8  0xb71689fb in KisSharedPtr<KisSharedData>::operator= (this=0x8765894, o=@0xa2caedc) at /home/boud/kde/src/koffice/krita/image/kis_shared_ptr.h:111
#9  0xb71980cb in KisWeakSharedPtr<KisImage>::operator=(KisWeakSharedPtr<KisImage> const&) () from /home/boud/kde/inst/lib/libkritaimage.so.7
#10 0xb71cc33f in KisPaintDevice::defaultBounds (this=0xaf808e8) at /home/boud/kde/src/koffice/krita/image/kis_paint_device.cc:322
#11 0xb71d0854 in KisPaintDevice::KisPaintDevice (this=0x8792508, rhs=@0xaf808e8) at /home/boud/kde/src/koffice/krita/image/kis_paint_device.cc:241
#12 0xb71d8ee6 in KisPaintLayer::KisPaintLayer (this=0x8990188, rhs=@0x87dfa10) at /home/boud/kde/src/koffice/krita/image/kis_paint_layer.cc:85
#13 0xb71d998a in KisPaintLayer::clone() const () from /home/boud/kde/inst/lib/libkritaimage.so.7
#14 0xb73b5af4 in KisLayerManager::layerDuplicate (this=0xa53b050) at /home/boud/kde/src/koffice/krita/ui/kis_layer_manager.cc:562
#15 0xb73c68bc in KisNodeManager::duplicateActiveNode (this=0xa53b110) at /home/boud/kde/src/koffice/krita/ui/kis_node_manager.cpp:416
#16 0xaed972a8 in KisLayerBox::slotDuplicateClicked (this=0xa09a3b8) at /home/boud/kde/src/koffice/krita/plugins/extensions/dockers/defaultdockers/kis_layer_box.cpp:411
#17 0xaed99f6d in KisLayerBox::qt_metacall (this=0xa09a3b8, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0xbfd9e3a8)
    at /home/boud/kde/build/koffice/krita/plugins/extensions/dockers/defaultdockers/kis_layer_box.moc:134
#18 0xb76aeb2d in QMetaObject::metacall (object=0xa09a3b8, cl=QMetaObject::ReadProperty, idx=48, argv=0xbfd9e3a8) at kernel/qmetaobject.cpp:237
#19 0xb76bdd80 in QMetaObject::activate (sender=0xa0bcaf0, m=0xb5bbe864, local_signal_index=2, argv=0xbfd9e3a8) at kernel/qobject.cpp:3295
#20 0xb59b0b9d in QAbstractButton::clicked (this=0xa0bcaf0, _t1=false) at .moc/release-shared/moc_qabstractbutton.cpp:206
#21 0xb567ad3d in QAbstractButtonPrivate::emitClicked (this=0xa0bcb08) at widgets/qabstractbutton.cpp:546
#22 0xb567bc8b in QAbstractButtonPrivate::click (this=0xa0bcb08) at widgets/qabstractbutton.cpp:539
#23 0xb567bf46 in QAbstractButton::mouseReleaseEvent (this=0xa0bcaf0, e=0xbfd9eac0) at widgets/qabstractbutton.cpp:1121
#24 0xb5763afd in QToolButton::mouseReleaseEvent (this=0xa0bcaf0, e=0xbfd9eac0) at widgets/qtoolbutton.cpp:721
#25 0xb52bfa7b in QWidget::event (this=0xa0bcaf0, event=0xbfd9eac0) at kernel/qwidget.cpp:8044
#26 0xb567abd0 in QAbstractButton::event (this=0xa0bcaf0, e=0x8206ac0) at widgets/qabstractbutton.cpp:1080
#27 0xb576665c in QToolButton::event (this=0xa0bcaf0, event=0xbfd9eac0) at widgets/qtoolbutton.cpp:1163
#28 0xb525ee3c in QApplicationPrivate::notify_helper (this=0x80a0498, receiver=0xa0bcaf0, e=0xbfd9eac0) at kernel/qapplication.cpp:4302
#29 0xb526663e in QApplication::notify (this=0xbfd9e7f4, receiver=0xa0bcaf0, e=0xbfd9eac0) at kernel/qapplication.cpp:3867
#30 0xb5d44d21 in KApplication::notify (this=0xbfd9f16c, receiver=0xa0bcaf0, event=0xbfd9eac0) at /usr/src/debug/kdelibs-4.4.4/kdeui/kernel/kapplication.cpp:302
#31 0xb76a971e in QCoreApplication::notifyInternal (this=0xbfd9f16c, receiver=0xa0bcaf0, event=0xbfd9eac0) at kernel/qcoreapplication.cpp:726
#32 0xb5265584 in sendSpontaneousEvent (receiver=0xa0bcaf0, event=0xbfd9eac0, alienWidget=0xa0bcaf0, nativeWidget=0x8630570, buttonDown=0xb5bc7018, lastMouseReceiver=..., spontaneous=true)
    at ../../src/corelib/kernel/qcoreapplication.h:218
#33 QApplicationPrivate::sendMouseEvent (receiver=0xa0bcaf0, event=0xbfd9eac0, alienWidget=0xa0bcaf0, nativeWidget=0x8630570, buttonDown=0xb5bc7018, lastMouseReceiver=..., spontaneous=true)
    at kernel/qapplication.cpp:2965
#34 0xb52f341a in QETWidget::translateMouseEvent (this=0x8630570, event=0xbfd9efcc) at kernel/qapplication_x11.cpp:4380
#35 0xb52f29c4 in QApplication::x11ProcessEvent (this=0xbfd9f16c, event=0xbfd9efcc) at kernel/qapplication_x11.cpp:3391
#36 0xb5320b8b in QEventDispatcherX11::processEvents (this=0x8053ac8, flags=...) at kernel/qeventdispatcher_x11.cpp:132
#37 0xb76a7d8d in QEventLoop::processEvents (this=0xbfd9f0f4, flags=) at kernel/qeventloop.cpp:149
#38 0xb76a81d9 in QEventLoop::exec (this=0xbfd9f0f4, flags=...) at kernel/qeventloop.cpp:201
#39 0xb76ad480 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1003
#40 0xb525eee4 in QApplication::exec () at kernel/qapplication.cpp:3581
#41 0xb77efd31 in kdemain (argc=1, argv=0xbfd9f274) at /home/boud/kde/src/koffice/krita/main.cc:49
#42 0x0804887b in main (argc=1, argv=0xbfd9f274) at /home/boud/kde/build/koffice/krita/krita_dummy.cpp:3

BUGDAY

I could not reproduce this bug. Unfortunately I couldn't try using CMYK due to crashes. I'm not sure if this is specific to particular color spaces.

I didn't get this issue at all. Switching between layers in the standard CMYK template was near instant. CMYK painting itself seems to lag noticably more than in RGB, but layer switching worked speedily for me.

TECH SPECS:
Krita revision 1166713
Kubuntu 10.04 32bit
KDE 4.5
QT 4.7.0 beta 2