[Pharo-project] OSProcess - can it pipe 1 MB?

I am trying to pipe roughly 1 MB of data into a program on Linux; I know it can handle the load, because I have tested it with by cat-ing a script and the data. I do not yet promise that my Pharo code is correct; if the program did not respond or returned junk, I would look to myself. But I am getting errors suggesting that AttachableFileStream is failing on writing to the pipe, and it's very suspicious that it simply can't handle the size of the string. Any ideas? Bill