@gominam1990: I saw the YT with Eng sub long time ago and to my recollection, at that time SH was in Taiwan.
It was on the We got married show with Seohyun. They were together when he called; he told SH that the two of them were going to sing this Banmal song or something like that and asked her to support them. SH answered of course, she would support.
*Just to be clear. I understand you mentioned Yongshin shippers. Although, I'm not a YS I like CNB and YH. SH is my focus.
So i think it's okay to share what i remember. Will try to find the link from my friend's collection.. Hope this is helpful.