Possible bug with Storage.open

This \1 at the end: is it expected?

Yes, that's expected. As you write more, you'll get a \2/etc. It's to allow the file to grow in size past that which is originally allocated. The files aren't really readable in the same way as other files.

I'll add something to the StorageFile docs.

so the generated documentation needs refresh?

The generated docs match the current stable firmware release - and .open is in one of the cutting edge builds :)

you should not write character code 255

It might - but honestly if you're writing binary files rather than text you're probably more likely to have read the docs and seen that. If you can think of other solutions for this I'm happy to look at them, but this seemed like the most stable way of handling 'growing' a file.