I've created a layout 960px wide with one right sidebar defined as 325px wide. When the home page displays, the center column, header, etc. take up the entire 960px and the right sidebar is squeezed into a narrow space to the right of the container table. The code looks correct to me, but the display is definitely wrong. Firebug reports the width of the sidebar as zero (0).
I've applied all the hot fixes I can find for 3.6.4 so it's certainly possible that I've introduced the problem myself, however, as I said, the rendered code when inspected in Firebug looks fine.
Is this a known issue? If so, what's the fix? If not, what suggestions do you have for troubleshooting it?
Btw, the same layout parameters work fine in v3.5.3.