The version of the paper "A Guided Tour of CLIM" in McCLIM's source tree, which I believe is updated to early 2006, states in section "A simple drawing application":

This is the first example that does not use clim-stream-pane (or one of its subclasses) as a pane class[*] [...]

[*] When using McCLIM, we have to do this as there are bugs in the behavior of clim-stream-pane that have not been fixed yet.

What are these bugs? Are they still outstanding?

Paolo