The AI will attack enemy infantry with as little regard to being silent as possible when the "Stealth" constraint is applied.
This means if they decide grenades are the best way to kill a group of soldiers, they will use them, despite how noisy they are.
Edit: They still do this. Not only do they use frags, but they also use smoke at times.
Create a group of soldiers, and have them wait in a position they will not be detected by enemy units. Let enemy units walk past, and change their ROE from Hold fire to Fire at will, free to engage.
Repeat this at least 3 times. Grenades *will* be used. Repeat the scenario over and over again, remove all grenades from stealth side and again with all grenades removed from enemy side.
Observe that when stealth side *has* grenades, they will use them despite the need for silence.
Mass closing ancient tickets with no activity for > 12 months; assume fixed or too trivial.
If this issue is still relevant in current dev build, please re-post.