Just started a new game so i'll test it out
Edit: So i just tried it on my current battle (in a cave, dark smokes and oozes and stuff)
test 1: cast muddle on green ooze, ooze had turn, attacked ian. Hawel cast blaze 2 on ooze, ooze next turn attacked ian.
test 2: cynthia cast muddle on green ooze, hawel cast freeze 1 on ooze before ooze has a turn, ooze still attacked (paige this time)
Test 3/4: cast muddle on dark smoke (it has MP), hawel cast blaze/freeze on it (2 seperate attempts) before smoke acts, smoke melee'd Ian.
So no luck on my current battle/difficulty (which is the default one, don't know what it is as i just skipped past it. oops).
Will try it on orc lord later, when I'm on that battle. Note this is all muddle 1 (as OP stated was used)