Slin: z-beating comes from too-small differences in the z values of two objects. The decal doesn't write into the z buffer, it's sufficient that the underground writes into the z buffer.

3run: When you can't get the z beating go away with better clip_near/far settings, then yes, contact Support with your level. It's quite possible that A7 had a different decal z offset, and thus behaved different. However such offsets are changed for a reason. Most likely, the A8 offset is better suited for most levels than the A7 offset.