Hello.. Is it just me or is Shift+Drag Drop deselecting some files for you too?
If I have 15 files (arbitrary number) in a folder and select them all,
then holds down Shift (move) while dragging the files then some of them
will be deselected and not moved to the destination.
PS! I noticed a thing..
It doesn't deselect, but rather remove the current selection and replace it with a new one starting from the item that is both focused and selected and to the item the mousecursor is above at the time of dragging.
Oh.. Newest, 9.1.1.8.
Detailed dual mode vertical with dual trees (I guess this is the most specific I can be).
It seems it does this no matter what filetype etc.
First I select files with either the mouse or by Ctrl+A, then press and hold shift and leftclick inside the selection, then drag it to its destination.
The deselection of files occurs immediately when I shift+leftclick.
If I only leftclick (no shift) it does what is expected (although that copies rather than moves).
That sounds normal & by design. You should hold shift after you click, else the click will be interpreted as a shift-click.
When holding keys to modify the drag & drop it only matters what is held down as you release the button, not what is held as you click the button. (When you click the button you haven't started dragging yet.)
It seems to be the same in Explorer and, I expect, just about everything. If shift is held down and you click then you're doing a shift-click range selection. The program has no way of knowing that you're going to drag the files out after clicking; it sees a shift-click, then a drag.