I've recently switched to a responsive style and some of my members are saying that the cursor sometimes jumps to a different place on the reply window inserting their reply into the quote or adding a smilie above the quote. Here is an example:
smilies always go before the "(quote)", never where the cursor is
The latter issue I have seen -- it's Android- and possibly keyboard-specific. It tends to relate to auto complete. Unfortunately, there isn't anything we can do about it short of not using the rich text editor. (I just tried to reproduce it on my Nexus 5 with Swiftkey and couldn't.)
I don't think I've seen the smilie issue (and couldn't reproduce it).
It's possible that these issues have been resolved in the most recent versions (I'm unsure if it's OS- or browser-related).