Picky keyframes!

Flash can be really picky sometimes, and I'd like to know why this is happening. I am using Flash MX 2004; I've done quite a bit with MX (not 2004), but I'm still fairly new to Flash in general.

Here's the predicament:

I have a motion tween. It goes from Frame 1 to Frame 26, and here the movie clip ends.

I made all my keyframes, selected them all, right click, and select "Create Motion Tween." Everything is good up to this point.

Then I go back to this movie clip later, and I want to add a frame at the end, so I right click and do "Insert keyframe." It automatically adds a motion-tweened keyframe. I don't want to tween this anymore, so I right click on the new keyframe and click "Remove Motion Tween." The keyframe turns gray, but there is no dividing line between the motion tweened frames and the new keyframe. Indeed, when I move the new keyframe around, the computer still interprets a Motion Tween!

If I right click on the last keyframe and the motion tween and select "Remove Motion Tween," then it removes the tween, but also turns the last frame of my previous tween gray!

I just want my little dividing line back!

I really hate it when programs assume they know what I want to do next.