[Camelot]

Good news, i can reproduce

Double-click on second last site, the site must see on Book View.
Then right-click on last site and merge or Ctrl+M (1-3×).
When click on the outsite last site = crash.

Here the gdb output:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff3bb1880 in QArrayData::shared_null ()
   from /usr/local/share/sigil/libQt5Core.so.5
(gdb) 
(gdb) bt
#0  0x00007ffff3bb1880 in QArrayData::shared_null ()
   from /usr/local/share/sigil/libQt5Core.so.5
#1  0x000000000061400e in TabManager::CreateTabForResource(Resource&, int, int, QString const&, MainWindow::ViewState, QUrl const&, bool) ()
#2  0x000000000061471a in TabManager::OpenResource(Resource&, int, int, QString const&, MainWindow::ViewState, QUrl const&, bool) ()
#3  0x00000000008659ed in MainWindow::OpenResource(Resource&, int, int, QString const&, MainWindow::ViewState, QUrl const&, bool) ()
#4  0x00000000008df600 in ?? ()
#5  0x00007ffff379ae7a in QMetaObject::activate(QObject*, int, int, void**) ()
   from /usr/local/share/sigil/libQt5Core.so.5
#6  0x00000000008cd575 in BookBrowser::ResourceActivated(Resource&) ()
#7  0x00000000008a7c74 in BookBrowser::EmitResourceActivated(QModelIndex const&) ()
#8  0x00000000008dadfe in ?? ()
#9  0x00007ffff379ae7a in QMetaObject::activate(QObject*, int, int, void**) ()
   from /usr/local/share/sigil/libQt5Core.so.5
#10 0x00007ffff79108a5 in QAbstractItemView::activated(QModelIndex const&) ()
   from /usr/local/share/sigil/libQt5Widgets.so.5
#11 0x00007ffff795e455 in QTreeView::mouseDoubleClickEvent(QMouseEvent*) ()
   from /usr/local/share/sigil/libQt5Widgets.so.5
#12 0x00007ffff76ee256 in QWidget::event(QEvent*) ()
   from /usr/local/share/sigil/libQt5Widgets.so.5

i attached my example epub
I hope this help.