Thanks for the information, I will try to find a fix for that. Maybe a dialog when snapping from/to IK that gives the options to clear keyframes from FK.
When pulling it needs to switch to FK, because I need to apply the pose to the FK rig. I think what you're describing is something going wrong when switching between IK and FK, because when IK is active while FK still has keyframes, then you can get very strange poses because of that. I thought about automatically removing keyframes but kind of didn't like that idea that much cause it could potentially remove stuff it is not supposed to remove.
If you want to animate in Blender using the IK rig, it is best to keep the pulling to a minimum. I imagined it mostly as a tool to get the initial poses and morphs (that is also why there is "Pull (Only Morphs)", so you can get the morphs without messing up the bone pose) into Blender, and then work from that and only push while working on the Animation.