unexpected behaviour for "git diff --word-diff"

Hi,

I get an unexpected behaviour for "git diff --word-diff" if 2 adjacent lines
start and end with the same letter. I tried versions 1.7.9 and 1.9.0.

Attached is a script with 7 examples. For each example, a file with 2 lines is
compared to a file with the same lines, only 1 or 2 letters appended in each
line. Each example is executed 4 times: with and without --word-diff-regex=.,
and with and without -R. The script prints the result of the diff of the 2
files. Just below it also prints the result of a counterexample: the same 2
lines with 2 lines (1 was sometimes not enough) of "xxx" between them.

Only for tests 5c,d and 6c,d the result matches the result for the
counterexample.

Kind regards,
Thomas