Clingo Printing Duplicated Answers?

I'm having trouble interpreting the clingo v 5.2.2 output below:

Why did clingo print answer1 twice? I've checked that the two answer1s are exactly the same.

I'm using optimization in my code. Could that be the problem?

I've set up a test repo. The above output can be generated by running the following line in the test repo.

clingo --opt-mode=OptN examples/swap-shift.lp

Here's what I understand now: with the --opt-mode=OptN option, clingo will try multiple models until it finds all the optimal models, and it will print all the models it has witnessed followed by the optimal models. I think that could explain why answer1 was printed twice in my original question.

In the output, I think Models is the number of total witnesses (including the first optimal model that got printed twice). Optimal is the number of optimal models found.

I made my observation by observing the output of this example

clingo --opt-mode=OptN asp/_all.lp asp/examples/scatter.lp

See how Optimization decreases and the two optimum models are printed in the end.