So I was reading through the original KG thread this week--the thread that ran here when the series originally aired on KBS. (I moved it into this board when the board was constructed, so it's here now on the last page.)
And it explains the big mystery of the series--why Yeohwa drifted off into pretty much irrelevance when it certainly seemed like she would be a central character throughout the series. Turns out that she had a DUI issue right before the series started, and there was a big pushback from viewers against her even being in the series at all. And apparently it didn't let up.
Judging from how the writers caved into pressure about the lack of correct historical names of characters, presumably they caved into pressure about the lead actress as well, and pulled way back on her character's involvement in the story.
I wonder what the original storyline was for Yeohwa. What a shame. And it looks like she's continued to have issues with alcohol since then as well. She's a good actress--sure hate to see that.
Also saw that the old guy who plays Biryu's father also got into some legal trouble and that's why we didn't see him for a while. I didn't really notice that he had disappeared since he wasn't a central figure, but yes he was away for some episodes and that's why.