Changing the Qt widget theme under Plasma's System Settings (Workspace Theme > Look and Feel) or LXQt's Configuration Center (Appearence > Widget Style) while having Konversation running with at least one active channel makes it segfault.

Reproducible: Always

Steps to Reproduce:
1. Open Konversation
2. Join a channel
3. Open System Settings > Workspace Theme > Look And Feel
4. Change the Qt plugin (if you have only one, then install Breeze or Oxygen) and click Apply

Actual Results:  
Konversation crashes.

Expected Results:  
Konversation should obey the change and apply the theme to its widgets automatically, as it happens to other Qt applications.

This is the segfault:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff1f28ced in QWidget::style() const () from /usr/lib/libQt5Widgets.so.5
(gdb) bt
#0  0x00007ffff1f28ced in QWidget::style() const ()
   from /usr/lib/libQt5Widgets.so.5
#1  0x00007ffff1efff91 in QApplication::setStyle(QStyle*) ()
   from /usr/lib/libQt5Widgets.so.5
#2  0x00007ffff1f00f06 in QApplication::setStyle(QString const&) ()
   from /usr/lib/libQt5Widgets.so.5
#3  0x00007fffe1154433 in ?? ()
   from /usr/lib/qt/plugins/platformthemes/KDEPlatformTheme.so
#4  0x00007fffe1160dfc in ?? ()
   from /usr/lib/qt/plugins/platformthemes/KDEPlatformTheme.so
#5  0x00007ffff13b9293 in ?? () from /usr/lib/libQt5DBus.so.5
#6  0x00007ffff0d0deb1 in QObject::event(QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#7  0x00007ffff1efe00c in QApplicationPrivate::notify_helper(QObject*, QEvent*)
    () from /usr/lib/libQt5Widgets.so.5
#8  0x00007ffff1f034e6 in QApplication::notify(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#9  0x00007ffff0cde89b in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#10 0x00007ffff0ce0c96 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#11 0x00007ffff0d34e33 in ?? () from /usr/lib/libQt5Core.so.5
#12 0x00007fffec7f49fd in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#13 0x00007fffec7f4ce0 in ?? () from /usr/lib/libglib-2.0.so.0
#14 0x00007fffec7f4d8c in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#15 0x00007ffff0d3523f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#16 0x00007ffff0cdc26a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)
    () from /usr/lib/libQt5Core.so.5
#17 0x00007ffff0ce420c in QCoreApplication::exec() ()
   from /usr/lib/libQt5Core.so.5
#18 0x00000000005c9f7c in main (argc=1, argv=0x7fffffffe278)
    at /home/paulo/Workspace/kde/konversation/src/main.cpp:160
(gdb)