AI Plan #5 in the units section of the Alphax.txt

[Dio]

As I was looking at making a pre-designed planet buster (I know, bad idea) I noticed that a planet buster weapon without the AI Plan#5 does not destroy a base and is instead considered a conventional payload with a weapon strength of 99. Also, a conventional payload with the AI Plan#5 acts as though it were a planet buster. I do believe this is a bug.

[Geo]

It's even worse with the tectonic -and fungal payload. Creating 'native' custom units with another chassis then missile, the 'native' AI won't detonate them.

[Yitzi]

There are a lot of cases where the "AI plan" is used to determine the actual mechanics of a unit.  All I can say is, don't give nonsensical AI plans.