I see. So no bug here?
Ah, my bad.... i interpreted your post completely wrong. sorry for that.
I thought you was questioning the (non-)sense between 0 vs 1 based indexing.
No, it is no a bug. The lines are stored inside an array and that array (list) is indexed starting from the number zero. However, we mortal humans have an issue with the number zero as normal kindergarten teaches us to start counting from 1, as does the caret position. So there is a discrepancy of 1. That is why there is need for the correction.