Signs and carpet do not drop when the underlying block is moved by piston

I tested all possibilities more extensively, and I've come to a different outcome than I expected. While assuming the sticky piston is always setup to immediately push against a solid block, and the sign and carpet is attached to that block, the following happens.

When the sticky piston is placed to extend upwards before powering:
On extend, sign will stay but carpet moves up with the solid block
On retract, sign will still stay but carpet drops because it's not attached to a solid block anymore

When the sticky piston is placed and powered to extend upwards:
On retract, sign and carpet both will pop off

When the sticky piston is placed to extend sideways before powering:
On extend, sign and carpet both will stay put
On retract, sign and carpet both will stay put

When the sticky piston is placed and powered to extend sideways:
On retract, sign and carpet both will pop off

With these results, I'm not sure anything is broken here.

Still an issue in pre-7.

Removed the old screenshot attachments since they were in part describing MC-17851, which was slightly misleading. Instead attached a video showing the inconsistency.

Now following the video clip, I see what is wrong, and it still happens.