Instant ready paratroopers?

Yeah, that's how it is supposed to work (with delay). Maybe it was a DIFFERENT paratroop unit which was flown into an airfield left intact, in that case the second unit only needs to refuel (while the first is still mobilizing).

This did not happen on an airfield, but at the line between two of my control points. It landed and started moving right away. No reorganisation symbol.

I have to say it was a pretty smart move that allowed him to attack my otherwise screened artillery from the back. To me it seems that the 6 hr delay only kicks in if you attack a control point. Up to now I even thought that wasn't possible to attack a line, but I think it's unbalanced if that kind of drop down somehow allows the paras to move.

A picture speaks a thousand words - can you post a screenshot of the problem?

Normally, paratroopers can not engage enemies until they have mobilized. While mobilizing, they can’t move, and can only defend. If they do anything else, you might have come across a bug.

That sounds amazing.

The other useful feature of border lines is that you can target them with nukes. If an enemy stack is within the kill radius of the nuke, bam bam!

Yes, I think that is what happened. He probably targeted my army. I must try it out.

However, I think it is wrong that it does not have a cooling down time.