[sjm217]

I feel this is a bit different. At least O_TRUNC is an option that is shown in documentation right next to the open() function so the programmer has the opportunity to spot it. With the FileSavePicker, there is no such option available and they have to add a line to manually truncate the stream. Also, open() is a low-level call, whereas FileSavePicker is the supposedly easy-to-use high level feature. I would say it is closer to fopen(), which does truncate by default.

[eviks]

These are very minor points. The main one is the same across platforms : bad defaults are common