For many years now, I've been using a highly-customized but antique style for LJ. AFAIK, the base style doesn't even exist any more, and mine has been hand-patched repeatedly to keep it running. Finally, a week or two ago, comment indentation suddenly stopped working, making my comments pages very difficult to read.
So I've finally given up and moved to a modern style. Still slightly tweaked here and there (for instance, I like being able to tell whether a conversation has new comments), but just a little extra CSS on top of a major theme, instead of a big custom blob.
None of which matters to anybody, unless you read comment threads in my journal and don't force your own style on them. That now works properly again. Might get a bit more tweaking (I don't love the pink on the comments page), but it's functioning properly...
[ETA: ... okay, the style had been working for *me* for many years. Apparently it's *never* worked for many other people. I had no idea. It must have been doing something right at the edge of HTML-legal, I guess...]