Dragging a file within a tab onto a directory is supposed to move it, not to copy it. Atm, the latter is the chosen behaivour, but in my opinion it is wrong. A workaround could be to right-click drag it, but we know that that doesn’t work.
You can hold SHIFT for move operation.
TotalC does it the same way.
Explorer indeed is moving directly and with CTRL it does copy.
We can make an option to inverse operations if it helps you.