Here is a test file.
Resize the window to be wide enough to hold all four boxes. Notice the container is no wider than the boxes, as intended.
Resize the window to be small enough that the boxes are on more than one line. Notice the container is the full width of the page (this is unintended).
Why? Is it possible to prevent this in a way that does not depend on the size of the boxes?
(Seen on Firefox 3.5 and Chrome 4.0.221.8. If a solution doesn't work in IE6, that's fine.)