Pin drag picking issue?

[pjcozzi]

See #16 (comment)

[pjcozzi]

Same issue in the eventListeners example.

[pjcozzi]

@bagnell can you look at this? Perhaps it is a multi-frustum issue where part of the billboard is overwritten during a pick? An alpha issue? Sizing issue?

[mramato]

I ran into this in Sandcastle as well, I actually filed CesiumGS/cesium#2461 for it