<Andreas>
Buffer streaming. It is very handy to be able to share the underlying
collection with a stream when you know what you are doing.
<Andreas>

Yes.  It would be even better to be able to do that wihout having to know so
much about what some other object might or might not do.

Damien is right.  Either Streams should ensure their internal collections
are unique to them, or they should assume that other objects have references
to those collections, and might be expecting the stream to always be
referencing the same collection.  The second approach can be implemented
using #become:.

--Alan