Basically, when choosing to "save" the file as a result of the editor not really being php friendly as kobra stated, the information may look like it is saved properly, but the file will not behave correctly. This "problem" is not necessarily something that is visible to the standard web page guest but is at the level of the bytes and data.

Basically errors can/will occur, it will seem like everything is correct, but there is information that is not displayed to the screen without other tools that will cause problems.

Further there are some text editors to also avoid if possible. Try to stay with the typical editors suggested on the site, they seem to work well nd why have any more headaches. :)