[testsfail] DragAndDrop.after_drag_finishes_pointer_events_no_longer_contain_handle

Intermittent test failure:

11:49:24 [ RUN ] DragAndDrop.after_drag_finishes_pointer_events_no_longer_contain_handle
11:49:24 [2017-07-17 11:49:24.432580] mirserver: Starting
11:49:24 [2017-07-17 11:49:24.432699] mirserver: Selected driver: mir:stub-graphics (version 0.27.0)
11:49:24 [2017-07-17 11:49:24.440282] mirserver: Using software cursor
11:49:24 [2017-07-17 11:49:24.440756] mirserver: Selected input driver: mir:stub-input (version: 0.27.0)
11:49:24 [2017-07-17 11:49:24.440918] mirserver: Mir version 0.27.0
11:49:24 [2017-07-17 11:49:24.442604] mirserver: Initial display configuration:
11:49:24 [2017-07-17 11:49:24.442662] mirserver: * Output 1: VGA connected, used
11:49:24 [2017-07-17 11:49:24.442703] mirserver: . |_ Physical size 0.0" 0x0mm
11:49:24 [2017-07-17 11:49:24.442733] mirserver: . |_ Power is on
11:49:24 [2017-07-17 11:49:24.442765] mirserver: . |_ Current mode 800x600 60.00Hz
11:49:24 [2017-07-17 11:49:24.442828] mirserver: . |_ Preferred mode 800x600 60.00Hz
11:49:24 [2017-07-17 11:49:24.442865] mirserver: . |_ Orientation normal
11:49:24 [2017-07-17 11:49:24.442895] mirserver: . |_ Logical size 800x600
11:49:24 [2017-07-17 11:49:24.442924] mirserver: . |_ Logical position +0+0
11:49:24 [2017-07-17 11:49:24.442955] mirserver: . |_ Scaling factor: 1.00
11:49:24 ../../test/drag_and_drop.cpp:652: Failure
11:49:24 Value of: count_of_handles_when_moving_mouse()
11:49:24 Expected: is equal to 0
11:49:24 Actual: 2 (of type int)
11:49:24 [2017-07-17 11:49:24.468282] mirserver: Stopping
11:49:24 [ FAILED ] DragAndDrop.after_drag_finishes_pointer_events_no_longer_contain_handle (38 ms)

https://mir-jenkins.ubuntu.com/job/build-2-binpkg-miral/arch=amd64,release=artful/64/console