wl_surface.leave event not emitted properly

The wl_surface.leave event is not emitted in the following scenario:

1. Run weston --output-count=2 nested under X11 (haven't checked with other setups).
2. Run WESTON_DEBUG=1 weston-terminal 2>&1 | egrep 'surface.*(enter|leave)'.
3. Start moving the weston-terminal surface into screen1, we get a proper enter event for screen1.
4. Move the surface completely into screen1, observe that no leave event is emitted for screen0.

Example annotated output:

# Surface is created on first output wl_output@13
[2544008.353] wl_surface@16.enter(wl_output@13)
# We start moving surface into second output wl_output@14
[2545425.727] wl_surface@16.enter(wl_output@14)
# Moved surface fully into second output, no leave event for first output!!!
# Moved surface fully back into first output, we get leave event for second output.
[2554513.085] wl_surface@16.leave(wl_output@14)

This is reproducible in both weston 10.0.1 (debian testing) and latest upstream (8f1ca820).

From a very brief investigation into weston internals there seems to be some rogue(?) weston_view for the surface that keeps the first output in its output_mask.