The clips a box touches are selected as it is dragged, and a clip that
leaves the box as it shrinks is deselected again, instead of the
selection only changing on release. Shift or Ctrl, held when the drag
begins, add to the selection the drag started with, as in the Project
panel. Escape cancels the box and puts that selection back. The
release still runs a single timeline.select, so the drag is one
selection change.
Brandon Thomas
Nigel Ihza Firdausy
ReReddo