Hi, this bug affects the "folder widget" and not "dolphin" (for which some related bugs were resolved long time ago). I can reproduce this behavior on current "Debian stable" (plasma-desktop 5.8.6; plasma-framework 5.28) as well as on "KDE Neon user edition" (plasma-desktop 5.10.4; plasma-framework 5.36): When you try to move files into subfolders while pressing the "shift-key", files get "copied" instead of "moved". So there is no difference between the "shift-key" and the "ctrl-key". This is very annoying and prevents efficient file management via desktop facilities. ...even more, when choosing "folder-view" to be the "default desktop layout" (what -- as of plasma 5.10 -- is the default setting).
Qt tries to determin the default action based on modifiers (e.g. Shift+Ctrl = Link). QXcbDrag does defaultAction(currentDrag()->supportedActions(), QGuiApplication::keyboardModifiers()) and QPlatformDrag::defaultAction() performs the check for keyboard modifiers. I'm quite lost as to why it works in Dolphin but not FolderView. I tried placing a qApp->queryKeyboardModifiers() before doing exec()'ing the QDrag but that didn't help. Also, at any point from what I can tell the keyboard modifiers QGuiApplication thinks of are indeed correct :/
Git commit 6b8fa112f47d6ed5794167b737007e35a7817746 by Kai Uwe Broulik. Committed on 14/09/2017 at 08:26. Pushed by broulik into branch 'master'. [Folder View] Fix supported drag actions SetSupportedDragActions is deprecated and doesn't seem to work. This fixes modifier shortcuts for dragging, e.g. dragging with Ctrl+Shift to create a link. FIXED-IN: 5.11.0 Differential Revision: https://phabricator.kde.org/D7798 M +5 -2 containments/desktop/plugins/folder/foldermodel.cpp M +1 -0 containments/desktop/plugins/folder/foldermodel.h https://commits.kde.org/plasma-desktop/6b8fa112f47d6ed5794167b737007e35a7817746