Command-tilde only toggles some pages

OS 10.6.8

Safari Version 5.1.7 (6534.57.2)

When I have just two pages open in Safari and use the Command-tilde shortcut, the pages toggle correctly. But when there are, say, four or more pages open, it will toggle only among 3 pages; I have to use the Windows menu to get to the other pages. The only pattern is that it will toggle every other time back to the original active page.

For example, if there are 5 pages open, it will toggle thusly:

1 > 2 > 1 > 3 > 1 > 2 >1 > 3 > 1...

pages 4 & 5 never become the active page. No matter how many pages are open, only 3 respond to the Command-tilde shortcut.

I have discovered that when I use Command-Shift-tilde, ALL the pages toggle through. The problem is that one has to contort one's fingers or use two hands to do it, which is clunky and really defeats the purpose of a keyboard shortcut.

So, my question is, is there any way to customize these shortcuts in Safari (or globally) to make Command-tilde toggle through all the pages and Command-Shift-tilde the back-and-forth one?