I noticed a weird thing...

[Mobhack]

Aha! - I got the little insect!

Your last purchase was a general support battery.

That left a global flag set - which then carried over to the AI purchase routines which misbehaved. Code was not clearing that properly between players (?). I'll squash that bug for the next release.

Meanwhile - the workaround is to ensure that the artillery mode is set to under command at the end of your purchasing, should you have bought D/S or G/S mode arty yourself.

NB (edit) - further testing, and it will only apply to auto-bought AI forces - there is protection in setting the artillery type variables in the purchase screen, so if you do this a human player (or the AI if you are buying for it) will only get the HQ at reduced cost, as the initialisation of the purchase screen ensures the globals are set correctly. The HQ is computer-bought before then autonagically though.