Ghosts of Minecraft

Hi, i thought that i filed this already yesterday, but i can't find it anymore, so here it is again. I am hosting a Spigot server MC and lately only three persons attended to it, including me. At one point yesterday one of the other three, let's call him Jort, said i had to come quickly, and saw with my own two eyes that a pictureframe with a sword on it turned all by itself. Earlier there was a huge hole in the road and i decided to repair it the old fashioned way, and wanted to place a last block of the curve where a fence should go up, so i placed a brick, and it got destroyed. I kept doing that but with altered intervals and everytime it broke away. I noticed in my presence bubbles appearing whilst i do not use potions etc, i find them unusefull when you are OP. Eventually i repaired the road. This is a strange behaviour that i never witnessed alone on my server. What is it, and do tell how to capture, destroy or excorsise this entity.