I just tried to reproduce this but I had no problems sneaking up on a stationary tank from behind (tried several times with both M1A1 and T72 in daylight) and place 3 satchels then crawl back and blow it up, the AI did not detect me once???
Do you have your specific testmission to share? What settings are you using (skill in editor and skill/precision in your cfg)? Are you testing with stock ArmA or maybe you have some addons loaded? Maybe you had other enemies around that spotted you?
/KC
I expirienced this several times in Multiplayer on different Servers... at least on one of them there is no AI related Mod active...
I tried in Singleplayer some minutes ago and it worked for me too, but Online I still got it... could this be lag related? I know some Animations are "skipped" in Multiplayer, but sometimes the turret of the Tank turns to my direction even when i stand behind a wall... the don't shoot, but they seem to spot me at least for about 30 secs... I'll test it a bit more... maybe it is just Desync or something...