After experimenting with Unk 0x237c in the Arsenal zero printout, (which also corresponds to unknown 3 in arsenal 3 Misc tab), I have concluded that it has something to do with unit actions, buttons, and mousclicks. By inputting various different numbers into it, I was able to get a few different results.
CODE
Unit used: Marine owned by player 1
value Results other units with this value
00 No attack button, larva
can't move, attack, patrol;
but can click
01 normal marine
02 normal marine medic
03 normal marine seige tank
04 normal marine probe/drone
05 normal marine SCV
06 can right click, but no action
walk, attack, hotkeys, no freeze
07-16 no right click, can move/attack
with hotkeys/buttons; right click
on other units/while in a group
crashes SC
Just a random thing I came up with. Anyone who wants to do more work with this is more then welcome. I didn't have stim packs researched, so I didn't test using it. That might be something else to try out. Also trying different numbers and different units.
//added
as a side note, the unknown AI action in both arsenal 3 and arsenal zero is stop. A way to see this is to set the unknown action to die, load up the units.dat in a mod then tell the unit to stop.