Since removal of tweak events 4986f71848,
box-select is activating while dragging files.
As far as I can tell this used to work because of differences
int the order tweak / click-drag events are handled.
Apply a workaround since dragging files doesn't prevent other parts
of the UI from activated (it's possible to open menus for e.g),
this is something we will likely want to limit which would resolve
this bug too.
13b6cec039