Version:            (using KDE 4.1.0)
Installed from:    Ubuntu Packages

I did search and noted this is a "known" issue but didn't find any for 4.1 on Ubuntu remix.
All I did was try to install Widgets from KDE-look.org.

Application: Plasma Workspace (plasma), signal SIGABRT
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread 0x7f0846b467a0 (LWP 5872)]
[New Thread 0x42b55950 (LWP 9582)]
[New Thread 0x4116c950 (LWP 9431)]
[New Thread 0x42354950 (LWP 5875)]
[New Thread 0x41b53950 (LWP 5874)]
(no debugging symbols found)
[KCrash handler]
#5  0x00007f08463ea095 in raise () from /lib/libc.so.6
#6  0x00007f08463ebaf0 in abort () from /lib/libc.so.6
#7  0x00007f0846424a7b in ?? () from /lib/libc.so.6
#8  0x00007f084642c08a in ?? () from /lib/libc.so.6
#9  0x00007f084642fc1c in free () from /lib/libc.so.6
#10 0x00007f08440b2b23 in ?? () from /usr/lib/libQtGui.so.4
#11 0x00007f0845318bcb in QObject::~QObject () from /usr/lib/libQtCore.so.4
#12 0x00007f08440b05f1 in QVBoxLayout::~QVBoxLayout ()
   from /usr/lib/libQtGui.so.4
#13 0x00007f08440ed06c in QWidget::~QWidget () from /usr/lib/libQtGui.so.4
#14 0x00007f0846099c0b in Plasma::AppletBrowserWidget::~AppletBrowserWidget ()
   from /usr/lib/kde4/lib/libplasma.so.2
#15 0x00007f08453110f0 in QObjectPrivate::deleteChildren ()
   from /usr/lib/libQtCore.so.4
#16 0x00007f08440ed104 in QWidget::~QWidget () from /usr/lib/libQtGui.so.4
#17 0x00007f0846099025 in Plasma::AppletBrowser::~AppletBrowser ()
   from /usr/lib/kde4/lib/libplasma.so.2
#18 0x00007f0845311014 in QObject::event () from /usr/lib/libQtCore.so.4
#19 0x00007f08440f2dd3 in QWidget::event () from /usr/lib/libQtGui.so.4
#20 0x00007f08440a554f in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#21 0x00007f08440aa125 in QApplication::notify () from /usr/lib/libQtGui.so.4
#22 0x00007f0845c17b71 in KApplication::notify ()
   from /usr/lib/kde4/lib/libkdeui.so.5
#23 0x00007f0845302109 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#24 0x00007f084530342b in QCoreApplicationPrivate::sendPostedEvents ()
   from /usr/lib/libQtCore.so.4
#25 0x00007f084532b0b3 in ?? () from /usr/lib/libQtCore.so.4
#26 0x00007f083fb25262 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#27 0x00007f083fb28516 in ?? () from /usr/lib/libglib-2.0.so.0
#28 0x00007f083fb289af in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#29 0x00007f084532b3af in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#30 0x00007f084412e72f in ?? () from /usr/lib/libQtGui.so.4
#31 0x00007f0845301585 in QEventLoop::processEvents ()
   from /usr/lib/libQtCore.so.4
#32 0x00007f08453016db in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#33 0x00007f0842dceecc in ?? () from /usr/lib/kde4/lib/libknewstuff2.so.4
#34 0x00007f0842dcf17d in KNS::Engine::downloadDialogModal ()
   from /usr/lib/kde4/lib/libknewstuff2.so.4
#35 0x00007f0846099267 in Plasma::AppletBrowserWidget::downloadWidgets ()
   from /usr/lib/kde4/lib/libplasma.so.2
#36 0x00007f08460998bb in Plasma::AppletBrowserWidget::qt_metacall ()
   from /usr/lib/kde4/lib/libplasma.so.2
#37 0x00007f0845316286 in QMetaObject::activate ()
   from /usr/lib/libQtCore.so.4
#38 0x00007f084409efa7 in QAction::triggered () from /usr/lib/libQtGui.so.4
#39 0x00007f084409f7b0 in QAction::activate () from /usr/lib/libQtGui.so.4
#40 0x00007f0844434caa in ?? () from /usr/lib/libQtGui.so.4
#41 0x00007f0845cb5195 in KMenu::mouseReleaseEvent ()
   from /usr/lib/kde4/lib/libkdeui.so.5
#42 0x00007f08440f34e0 in QWidget::event () from /usr/lib/libQtGui.so.4
#43 0x00007f0844432a21 in QMenu::event () from /usr/lib/libQtGui.so.4
#44 0x00007f08440a554f in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#45 0x00007f08440aa329 in QApplication::notify () from /usr/lib/libQtGui.so.4
#46 0x00007f0845c17b71 in KApplication::notify ()
   from /usr/lib/kde4/lib/libkdeui.so.5
#47 0x00007f0845302109 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#48 0x00007f08440a7455 in QApplicationPrivate::sendMouseEvent ()
   from /usr/lib/libQtGui.so.4
#49 0x00007f084410991b in ?? () from /usr/lib/libQtGui.so.4
#50 0x00007f084410866b in QApplication::x11ProcessEvent ()
   from /usr/lib/libQtGui.so.4
#51 0x00007f084412e8f3 in ?? () from /usr/lib/libQtGui.so.4
#52 0x00007f083fb25262 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#53 0x00007f083fb28516 in ?? () from /usr/lib/libglib-2.0.so.0
#54 0x00007f083fb289af in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#55 0x00007f084532b3af in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#56 0x00007f084412e72f in ?? () from /usr/lib/libQtGui.so.4
#57 0x00007f0845301585 in QEventLoop::processEvents ()
   from /usr/lib/libQtCore.so.4
#58 0x00007f08453016db in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#59 0x00007f08444370e5 in QMenu::exec () from /usr/lib/libQtGui.so.4
#60 0x00007f0844441900 in ?? () from /usr/lib/libQtGui.so.4
#61 0x00007f0844441d38 in QPushButton::qt_metacall ()
   from /usr/lib/libQtGui.so.4
#62 0x00007f0845cc16d5 in KPushButton::qt_metacall ()
   from /usr/lib/kde4/lib/libkdeui.so.5
#63 0x00007f0845316286 in QMetaObject::activate ()
   from /usr/lib/libQtCore.so.4
#64 0x00007f08443ac24e in ?? () from /usr/lib/libQtGui.so.4
#65 0x00007f08443ac873 in QAbstractButton::mousePressEvent ()
   from /usr/lib/libQtGui.so.4
#66 0x00007f08440f3667 in QWidget::event () from /usr/lib/libQtGui.so.4
#67 0x00007f08443ace20 in QAbstractButton::event ()
   from /usr/lib/libQtGui.so.4
#68 0x00007f0844441b78 in QPushButton::event () from /usr/lib/libQtGui.so.4
#69 0x00007f08440a554f in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#70 0x00007f08440aa329 in QApplication::notify () from /usr/lib/libQtGui.so.4
#71 0x00007f0845c17b71 in KApplication::notify ()
   from /usr/lib/kde4/lib/libkdeui.so.5
#72 0x00007f0845302109 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#73 0x00007f08440a7455 in QApplicationPrivate::sendMouseEvent ()
   from /usr/lib/libQtGui.so.4
#74 0x00007f0844109756 in ?? () from /usr/lib/libQtGui.so.4
#75 0x00007f084410866b in QApplication::x11ProcessEvent ()
   from /usr/lib/libQtGui.so.4
#76 0x00007f084412e8f3 in ?? () from /usr/lib/libQtGui.so.4
#77 0x00007f083fb25262 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#78 0x00007f083fb28516 in ?? () from /usr/lib/libglib-2.0.so.0
#79 0x00007f083fb289af in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#80 0x00007f084532b3af in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#81 0x00007f084412e72f in ?? () from /usr/lib/libQtGui.so.4
#82 0x00007f0845301585 in QEventLoop::processEvents ()
   from /usr/lib/libQtCore.so.4
#83 0x00007f08453016db in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#84 0x00007f0845303729 in QCoreApplication::exec ()
   from /usr/lib/libQtCore.so.4
#85 0x00007f084673623b in kdemain ()
   from /usr/lib/kde4/lib/libkdeinit4_plasma.so
#86 0x00007f08463d61c4 in __libc_start_main () from /lib/libc.so.6
#87 0x0000000000400649 in _start ()
#0  0x00007f0846455b81 in nanosleep () from /lib/libc.so.6