I think Steven is right , this is about redefining or not. When you insert a block without path , AutoCad uses the block definition allready present in active drawing. If you put a path to it , AutoCad will overwrite current block definition with the one on file. So , if you insert block for the first time , then edit it and after that insert the one from file , your edited definition will be overwritten again. Standard / classic / basic AutoCad behaviour.