Visible portion of backdrop different in 2.0 vs. 3.0

[jwzimmer-zz]

Expected Behavior

The backdrop should display like it does in 2.0; the sky and ground should extend to all edges.

Actual Behavior

The bushes extend to the right edge, but the sky and ground don't, leaving a white strip.

Reported by @fsih during the Catch Game internal playtest (6/2/17):

Backdrop has white edge on right side

Steps to Reproduce

Choose the backdrop shown in the screenshot.

Operating System and Browser

Mac OS, Chrome