There is another issue connected with this problem:
1) If your mate reply "Negative" to your "Engage" order, the order is sometimes not cancelled and your mate is still in engage mode. Moreover, if you then give your mate some other target he will automatically try to engage this new target as if "Engage at will" command was given.
2) It seems as if a direct LOS and/or distance to a target are the reasons for AI unit refusing to even start the engagement. This conclusion is apparent from the repro mission "AI_engage_bug_AT_test.Stratis_2.zip".
More info on the LOS and distance testing (22.4.2014):
- if there is a terrain or object blocking LOS of an unit which is supposed to engage a target, the engage process is not started at all (most of the time*)
- the distance between the engaging unit and its target might be an irrelevant factor after all but it will need more testing to confirm
* Sometimes the unit is able to start executing the engage process even if a terrain or object is blocking its LOS but will fail if the unit is not able to get direct LOS in few seconds after the start of the process. Sometimes the unit will run far far away in irrational directions.
Observed in Dev Beta 0.77.0.109751, Dev 1.09.114055 and Dev 1.19.123859.