fmincon chosing values out of bound

I was using fmincon solver for minimizing a non linear function. I
have noted that sometimes for some in between iterations it choses
values lower than the lower bound for decision variables and then
later after few iterations it gets lost somewhere. Can anyone give a
reason for same? could it be an indication of infeasible problem but
then it doesn't come out with exit flag status -1. I had to finally
kill matlab from task manager
.

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