It's been happening to me under Safari, and it seems to have something to do with by browser window width. If I make the window wide enough, the rest of the sidebar comes back, without my having played any games with the cache or reloading.

I suspect a Safari CSS rendering glitch. The next step I'd take in hunting down details is investigating whether AppleScript (or something) could return the width of the browser window, then I'd narrow down exactly what value makes the trouble. But I've just realized that it's a bright, sunny day and I haven't been out of doors since Friday and I need some exercise. (OK, here's a script that full-sizes the Safari window; poking around in it might reveal some useful commands.)

But I'm not using Safari: I'm using Mozilla and it happened to me. In fact, it's happened again and clearning the cache and reloading didn't work this time. However, I'm wondering if my version of Mozilla is starting to get really wonky because I can't get -- wait a minute. I just clicked on the re-size thingy and that did work. My window size has been being a little odd for a while now. Something somewhere is not working quite right, but I'll be dammed if I know what or even where.

MKK

I wouldn't worry too much about it - your audience can make it work and there are other things some of your readers find at least that annoying. Personally I run a decent sized screen (nominal 22") high resolution monitor at high resolutions so my pixels are relatively small and close together. I find the style sheet choices generally a nuisance - frex
.blogbody {
9font-family:georgia,serif;
9font-size:14px;
9font-weight:normal;
9line-height:19px;
9padding-left:10px;
9padding-right:10px;
9padding-top:10px;
9padding-bottom:10px;
9}
Granted that georgia is a good screen font, it's not my choice for on screen reading and even when I impose a bigger font-size I have to also tinker with the leading (line-height:19px) and so on. I don't suppose it's your taste in music but I'll go with Garden Party on this one - please yourself and let the rest of us make it work it's your blog. Point is the more control you apply (what I think of as the print orientation of total control) the more likely something is to break on an enthusiast's setup. No point in trying for total control and total compatibility is there?