Tiles erased while hovering over them

I was drawing forest tiles trying to reproduce a map. I was switching between different tiles and made a mistake. I tried to use the eyedrop tool to pick tiles and to copy them 1 hex away (where I wanted them to be). The eyedrop tool seemed to freeze (not picking the forest tile), I then tried to pick a river tile (wich worked). Then I picked the forest tile I wanted to move (it worked), but when I hovered over other tiles they disapered. However the "hovering-deleting effect" seemed to be limited to a portion of the map. I hit CTRL+Z to undo it worked several times until it didn't (I have no idea why). Trying to understand what hapened, I randomely set the tile I had selected on newly emptied tiles, then hovering over and hitting CTRL+Z This could be linked with me often trying to zoom in/out with the scroll button, even if I know this is not the function of the scroll button (I'm used to scroll in/out to adjust zoom, it's not something that I will forget soon :) ), but when the bug occured I was working with individual tiles. I noticed that the scroll level seemed to be registered somewhere because when I switched to non-individual-tiles drawing I ended up with a radius of 5/6 tiles available for drawing and the tiles erased seemed to be approximately limited to the area of the radius I saw then. Maybe I "drawed" a radius of individual tiles and somehow creating "ghost tiles", allowing the bug to occur.