This has recently started happening, not just for me but for everybody who tires it. When we place a block in a certain area - It drops our fps and laggs? Any ideas?
This is a quick set of timings I did whilst placing the laggy blocks. http://timings.aikar.co/?url=11316877
Worldedit will always cause some lag when you use. Just restart the server and don't use it again until necessary.
Does it happen, when you are trying to place blocks in a void area (no blocks bellow the block you have placed)?