Completion and partial width windows

A colleague pointed this out. Split a frame vertically to get two side-by-side windows. Assume that truncate-lines is T and truncate-partial-width-windows is T, the defaults values, I think. Do a C-x b TAB to try to complete on a buffer name. If the number of buffers is very large and the windows are narrow, many of the buffer names are not visible because the lines have been truncated. There's no way, using the keyboard, to see names that have scrolled off to the right. On a normal full-width screen, pressing tab causes the completion window to scroll so you can see more. Should we momentarily bind truncate-lines and truncate-partial-width-windows to NIL for any completion window? This bug doesn't happen in 20.4. Ray