Does anyone know why ReadWriteStream overrides #contents from WriteStream?

WriteStream behaves as I would expect

   |stream| stream := WriteStream on: String new.

   stream nextPutAll: 'chris'; reset; nextPutAll: 'C'; contents     "--->  'C'   as expected"

but ReadWriteStream doesn't...

   |stream| stream := ReadWriteStream on: String new.

   stream nextPutAll: 'chris'; reset; nextPutAll: 'C'; contents     "---> 'Chris'   unexpected!"

I want to reuse a ReadWriteStream, so I want #contents to honor the end position.  What's going on here?