Hey,
I just tried mass-changing the track width of all selected tracks. I selected a bunch of them (by ctrl+clicking), then right-clicked on a track and chose "Attributes...". In the popup I changed the track width, and then clicked "Update". This breaks the tracks, as it moves certain nodes far away in a top-left direction. This is easily reproduced by creating a new blank PCB, drawing two tracks, and using the approach described.
Hopefully this can be fixed soon, as I have a lot of tracks to resize :/
Sybren
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
