https://github.com/fuzziness/kabeja/blob/f126b44ac32962004217be53bfca59fd989fcb95/blocks/dxf/src/main/java/org/kabeja/dxf/parser/entities/AbstractEntityHandler.java#L61 The static lastLayer here causes problems in multi-threading environment. It leads to ConcurrentModificationExceptions and probably unwanted behavior.