So I had never once select the heart icon when talking to her before... After completing her "A New Path" quest (post patch) and I went back to the Hawke Estate... Merrill was there. Hawke and Merrill then argue a little bit (I have 100% rivalry with her) but then there is an option with a heart icon and a heartbreak icon. The heart icon leads them to sleep together while the heartbreak icon has Hawke saying something like "You can experiment all you want as long as it does not endanger Kirkwall" in which she stormed off.
I'm not sure if this is a bug or not, her appearing out of the blue wanting to made it up all with Hawke when I had never expressed any interest in her before
BTW, this only happened in my 2nd playthrough (Hawke is on Fenris friend-mance) and my bf's playthrough (Izzy's friend-mance) but it didn't in my first (Anders friend-mance and moved in). Anybody got this scene and feel weirded out?