You have Thermal relieve activated in the pad connection settings of the zone. Switch this to solid.
To get to this dialog (in open gl canvas) left click on the zone outline to select it and then press E, or right click on the zone outline and select properties from the menu that pops up.
(Switching to open gl is done with F11 or via the view menu. I don't know how this is done in legacy because i never used that canvas.)