According to the linked sup-devel thread, a similar fix has been merged to
master(?).

Can you check if the bug is still valid?

A patch for this has been posted on sup-devel

http://rubyforge.org/pipermail/sup-devel/2010-February/000366.html

BufferManager.ask truncates responses to (terminal width - question length).

The easiest way to test if this happens in your environment:
* open a search \ 
* hold down aaaaaaaaaabbbbbbbbbbbcccccccccccc and so on until you've wrapped
across the terminal width a few times
* refine search |
* (you may need to left-arrow a little to see anything)
* the string you are refining should be truncated where your cursor first went
beyond the terminal width in the original search

This does not happen for everyone.

git next
ruby 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin10]
ncursesw (1.2.4.1)