Forgive me if this isn't the right place to pose this question. I do need guidance on this.
In 2018 I had submitted a paper to a refereed journal. It had gotten accepted for publication by said refereed journal modulo some minor revisions and I am in the process of revising it. I also had presented this result at the 2019 Symposium On The Theory Of Computing [STOC 2019] in June. So far so good at this point, plenty of papers have appeared in both the conference proceedings--to disseminate quickly, and then in polished revised form in a refereed journal a bit later.
Here is where my dilemma is. This past fall 2019 I also received an invitation to submit this same result to a special edition of STOC 2019, which will appear in the SIAM Journal Of Computing. I had said yes thinking that this was just like the Conference Proceedings, without realizing at that time, that there may be a moral dilemma. I am not sure if I would be double-publishing my paper, which I understand is a no-no.
I am not sure where to go from here. I explained the situation to both the editors of the refereed journal and to the committee that invited me to submit this result to the special edition of STOC 2019, but have not received guidance back.
So this is my question: What do I need to do. I want this paper to go into the refereed journal, as they were the ones who reviewed it first. I admit to not being that familiar with the rules of publishing in academic journals. Thanks in advance for any guidance!