Simple tweens with waits? Unexpected results.

I'm trying to simply move an object (an eye) to a position and then back again at random times however with the code below the eye movement speeds up and seemingly the Trigger_Eye_Movement function is getting run over and over again. I do not understand this as it should only get triggered once the tweeen (look centre from right) has finished..

I thought I knew how the wait system worked but clearly something is going terribly wrong. It seems like this should be something very simple to do.

It seems the issue might be with tags. I think if the tween finished contains ANY word from the tag then it triggers. I set each tag to just "centre" and "right" and now seems to work..

Are there many instances of this eye sprite or just one? With multiple instances, I guess the "Tween finished" event may trigger separately for each instance, which will cause multiple function calls. And there will be more and more such calls with each iteration.