Yup, I'm seeing the same problem. It affects all JSPs afaict. Has this really been around for over a year??
Hmm... this seems related to another bug.
If you use a capitalized .JSP for a .jsp file in Windows, it will reveal the source code. Haven't tested it on a Linux machine, so I don't know if these bugs are Windows-specific. If so, it may be some sort of mismatch due to Window's case-insensitivity. Probably matches a filename check but fails an exact search, so it gets interpretted as a html/text content. That's my gut suspicion...
Another possibility is that there's an error in the code with respect to the matching. I'll know more once I try it on Linux.
Anyone know offhand what package the source with the bug might be in? If so, I may try fixing it.