Version:           3.5.8 (using KDE KDE 3.5.8)
Installed from:    Debian testing/unstable Packages
OS:                HP/UX

When i try to change proxy server from a konqueror toolbar panel button konqueror krashes. But changing proxy server using a menu works fine.
So, start the konqueror and click the proxy change button to chush it. Is you first chenge proxy by menu the proxy change button will work well before you restart konqueror. here is the crush report

[KCrash handler]
#6  0xb74d2d67 in QGArray::QGArray () from /usr/lib/libqt-mt.so.3
#7  0xb783e12f in KConfigBase::readEntryUtf8 () from /usr/lib/libkdecore.so.4
#8  0xb78415e9 in KConfigBase::readNumEntry () from /usr/lib/libkdecore.so.4
#9  0xb5a13907 in SettingsPlugin::toggleProxy ()
   from /usr/lib/kde3/libkhtmlsettingsplugin.so
#10 0xb5a14792 in SettingsPlugin::qt_invoke ()
   from /usr/lib/kde3/libkhtmlsettingsplugin.so
#11 0xb71deb10 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#12 0xb71df5f5 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#13 0xb6bd7169 in KAction::activated () from /usr/lib/libkdeui.so.4
#14 0xb6c161e2 in KAction::slotActivated () from /usr/lib/libkdeui.so.4
#15 0xb6c16344 in KToggleAction::slotActivated () from /usr/lib/libkdeui.so.4
#16 0xb6c1617c in KAction::slotButtonClicked () from /usr/lib/libkdeui.so.4
#17 0xb6d05068 in KAction::qt_invoke () from /usr/lib/libkdeui.so.4
#18 0xb6d059de in KToggleAction::qt_invoke () from /usr/lib/libkdeui.so.4
#19 0xb71deb10 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#20 0xb6c0ead4 in KToolBarButton::buttonClicked () from /usr/lib/libkdeui.so.4
#21 0xb6c0eda3 in KToolBarButton::mouseReleaseEvent ()
   from /usr/lib/libkdeui.so.4
#22 0xb7215460 in QWidget::event () from /usr/lib/libqt-mt.so.3
#23 0xb6c50b91 in KToolBarButton::event () from /usr/lib/libkdeui.so.4
#24 0xb717336a in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#25 0xb7175522 in QApplication::notify () from /usr/lib/libqt-mt.so.3
#26 0xb7883622 in KApplication::notify () from /usr/lib/libkdecore.so.4
#27 0xb710473d in QApplication::sendSpontaneousEvent ()
   from /usr/lib/libqt-mt.so.3
#28 0xb71033eb in QETWidget::translateMouseEvent ()
   from /usr/lib/libqt-mt.so.3
#29 0xb7101858 in QApplication::x11ProcessEvent () from /usr/lib/libqt-mt.so.3
#30 0xb711867c in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#31 0xb718e6e4 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#32 0xb718e3e2 in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#33 0xb7174f13 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#34 0xb64fdd64 in kdemain () from /usr/lib/libkdeinit_konqueror.so
#35 0xb7f16454 in kdeinitmain () from /usr/lib/kde3/konqueror.so