Mouse events report incorrect position when 2nd level parent is offset. #1744
Description
I've also reported this over at mapbox here: mapbox/mapbox.js#411 as it seems that they have this problem in an early version of leaflet.
The issue is that mouse events are offset when a 2nd (or third or fourth) level parent is offset vertically.
It appears that the event position is calculated based on the screen position + the scroll area. When the map element is positioned relatively it does not properly calculate its vertical offset when getting the coordinates of the mouse event.
I'm working on a pull request to fix this