diff -u produces inconsistent header when comparing to a 1-line file

[Aaron Bentley]

Here's an example:
$ echo hello | diff -u - /dev/null
--- -   2005-02-09 12:08:11.000000000 -0500
+++ /dev/null   2004-02-26 20:16:33.000000000 -0500
@@ -1 +0,0 @@
-hello

The -1 is not a comma-separated pair, but for all other sizes it is a 
comma-separated pair.  Note that 1,2 is used for a two-line file, and 
1,3 is used for a three-liner, so 1,1 would be the expected value.

I have been unable to find a spec for the unified diff output format, so 
I can only guess at what's a bug.  If it's not, are there other cases to 
which this header format applies, or a spec I can read?

Aaron

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Aaron Bentley
Director of Technology
Panometrics, Inc.