I suspect this is more to do with latency than anything else, ie. if you have higher latency, you could get tagged for the auto, before the debuff expires. Of course, being a tester, you have very minimal latency, so these issues do not come up, meaning you can make the time between the debuff wearing off and the first auto as small as possible.

In theory, this should be a learning point for the battle team to test buff/debuff timers and potential one shot hits in a range of different latency scenarios, just to make sure nothing like this happens again.