It could be due to the arguments that come after '-w'

If this would be the reason, I think it should fail every time, and not run well most of the time. There are actually two arguments after the -w: The first is a Windows UNC path, and the second is just a word. Aside from the path separators, only letters and digits are used in the arguments. Nothing dangerous about quoting anyway.

The error message seems to be generated pretty late. I am using redirection, i.e.

run([....],'>output','2>error');
[download]

and the error message of run() is found in the output file, which means that it is generated after run() has set up the redirection. I don't know whether this gives us some clue though....