I got the same problem to. I recognised that my entitis are too small to allow a correct collision detection. I tried to scale the level including all entities to bigger size but only the blocks are affected.
What can I do to scale a whole level ( all blocks, all groups, all entities/models, all sprites etc ) at once ?
You can select all entities together in WED with the mouse and scale them all together.But after that you have to place the entities new! I think an easier way is not possible because the different origins.