While I won't dismiss the notion that the tree may be getting damaged in some way, you also have to keep in mind that file reordering within Sigil works without crashing on many Linux distros with many versions of Qt5--including some with KDE/Plasma DEs. The only two that have reported crashes when reordering are PCLOS and now Mageia. Which leads me back to the custom platform Qt plugin being the problem on those distros where reordering actually leads to crashing.
|