Flat-ended buffers not flat

I am trying to construct flat-ended buffers along overlapping line segments. I need to be able to buffer the line width independently of the line length. That is, I do not want the additional length that is added with the round buffer ends because I need to be able to create a buffer that is wider (e.g., 800-m width) than it is long (e.g., 400-m long). I thought this would be quite simple.

I made my buffers with flat ends using the buffer analysis tool.
Unfortunately, I have the same problem that Dan Austin reported in January 2009. Here are my buffers with a problematic one selected:
Attachment 22577

Is there a solution for this yet? If not, has anyone figured out a work-around? I've got thousands of these buffers, so manually editing them isn't really an option.

Thanks!

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