I think it might be related to it being multi combat, so if lesser starts attacking you and you start fighting back, near its death the bot will select someone else to attack without finishing off the lesser because from what I assume it wasn't the target the bot chose
So it's down to it being agro monsters I think, mainly because once the agro is over and it's only the client choosing the targets it's all fine
Either way, thanks for your time and this pic was taken right before I replied
(The first one attacked me and right before it was going to die, the bot began attacking the 2nd lesser)
Edit: Never mind.. Agro was over and yet it still happened but it took ages for it to happen this time.. so not even sure anymore