Hello,
I was copying smth from MemoryCard to MyDocs using the builtin Fileman.
Then, when it started, it hung and I restarted the N900. Then, MyDocs became read-only, which fixed itself(I didn't touch anything) after connecting to PC.
But, Mydocs and Memcard and files in them became rwxrwxrwx permissions. It is not anything dangerous, but it annoys. Chmod doesn't work.