I think is not normal , i do insert normal keyframes and only one object gets this line.
What is it?
It is a long keyframe, showing that the keyed value remains the same until the fraome at the end of the long bar. This was added into the 2.43 release as an improvement to the animation tools. I have files I created with 2.42a, and the only difference when I open them in 2.43 is the bar you are talking about, but the animation runs the same.
Keep blending!!