[RMMV] TILE COPYING ISSUE

My RPG Maker MV is giving me a hell of a time. I cannot copy multiple tiles at once. For example, if i copy a 4x4 area using right click, and then if i paste it somewhere else using left click, only the first tile (the upper left tile) gets coppied. It was working before, but now suddenly it is messed up! I dont know what has gone wrong. Is there any way to correct this?