[Pharo-project] Unix thing? Possible silent failure writing file.

I just had another silent failure that is a little disturbing. In short, I was writing a text file for use with R, needed a new column, arranged for it and re-wrote (so I intended) the file. Nothing happened, and no errors resulted. Is there a unix newbie trap at work? Truncating the file allow it to work. The need for that is one thing; having writes fail with no trace of why is another. Any ideas? Bill