Footer background not extending down with standard theme

Issue report by Christopher Upton

Product

FileMaker Pro

Version

12.0v4

Operating system version

OS X 10.8.4

Description of the issue

The 'background' portion of the footer is not displaying in a standard theme (I'm using River, but have tried changing to Quarry and it behaves the same)

Steps to reproduce the problem

drag the bottom edge of a window downward to increase its size

Expected result

proper rendering

Actual result

see screenshot

Configuration information

It works fine for a while, but changing something in the layout causes it to go wrong and then the only way I've found to fix it is to recreate the layout from scratch. I haven't worked out what specifically causes it, but the last change I remember was dragging items (including a portal) into a tab control which covers most of the body section. I made sure nothing is touching the edges of the sections or tabs. I even dragged the entire tab control out onto the scratchpad area leaving nothing in the body or footer and it still behaves the same.

Screenshot