Resolves: #i123765# reset buffered DropTarget when undocking

(cherry picked from commit 8d679227fafe9108c4dc6e8adff85a727e4ef3af)

Change-Id: Ia6fba705d91157afea30693fa7078aabc96f02ac
(cherry picked from commit 032a4f6b2d771dd4e1b4a1ceee7c3ef15ca356eb)