[bug-diffutils] Bizarre failure of -I to ignore lines

[Davis Herring]

(First, apologies for the significant size of the attached files; I
managed to trim 85% of their content before I could no longer reproduce
this behavior.)

Comparing the two attached profiling files with "diff -I calls m1.dat
m2.dat" (using diff version 2.8.1) produces

3254,3256c3254,3256
< Norm
< There were   calls in    1.259 s.
< There were   calls in    1.040 s.
---
> Norm
> There were   calls in    1.249 s.
> There were   calls in    1.034 s.
7623,7625c7623,7625
< Norm
< There were   calls in    1.255 s.
< There were   calls in    1.044 s.
---
> Norm
> There were   calls in    1.272 s.
> There were   calls in    1.060 s.

even though no line is changed that does not contain "calls" and many
lines are changed that do (a straight diff is 4420 lines).  Adding
--minimal makes it go away, as do various changes to the file.

Am I asking too much of the -I option, or is this a bug?  (It would seem
the latter since it identifies the "Norm " lines as changed in the
output even though they are identical.)

Thanks,
Davis Herring

-- 
This product is sold by volume, not by mass.  If it appears too dense or
too sparse, it is because mass-energy conversion has occurred during
shipping.

m1.dat
Description: Text document

m2.dat
Description: Text document