Weird lane behaviour - user error or bug?

Not worked this out clearly enough to file a problem report, just wondering if anyone else has seen this and / or knows of a cause.
 
This is happening all over a couple of recent projects, but to give an example: I've just been trying to edit an audio clip. This is one clip on one track, no extra lanes. I position the now time marker and press S for Split. I now have two clips; one the un-split full-length clip, the other just starting from the split point. If I open the take lanes for the track, I see that a new take lane containing the shorter clip has been created.
 
Is there any sensible reason why this would happen? Have literally never seen it before.