Some node configurations in Shake 4 may result in imagery that appears to have horizontal lines on some edges, resembling interlace artifacts, as seen in the following illustration:
One way around this is to apply an Other-Bytes node to promote affected nodes to 16 bits. This should remove the artifacts. You don't need to apply it to the entire script, just to the areas you find the behavior occurring.
The script in the following illustration shows a scenario where you might notice the artifacts. The RotoShape fills half the screen, and the Primatte is set to a primary scrub of blue.
In the next illustration, an Other-Bytes node is introduced before the QuickPaint node, and the artifacts do not occur:
Note: A side-effect of this using workaround results from Shake's internal tree optimization: You cannot demote the script to 8 bits with a second Other-Bytes node until after the Max1 node (in the example script above). Placing it above Invert1, Inside2, or Max1 will not remove the artifacts.