Split at playhead seems to mess with keyframes

I have 30-odd video tracks (headshots of people singing) which have size/position keyframed on them so I can move them around the screen in different configurations. The changes are discrete keyframes, not linear/smooth.
If I have for example a 3-minute track with discrete keyframes at 0s and 60s, and then I split the track at 120s, it removes the 60s keyframe and inserts a new keyframe with blank data around 30s. In this case (size & position) “blank data” means width == height == top == left == 0.
I can’t work out whether this could be expected behaviour (perhaps I’m misunderstanding something about keyframes?) but I’d have expected the split to maintain existing keyframes.