I introduced problem by fixing a typo in a comment in a zone file.
The character positions or file sizes of the file were hardcoded
in the unit test. I had seen the failure on my system but didn't
associate it. (My mistake for not looking closely.)

The typo fix added one character so changed the hardcoded 549 to 500
and 506 to 507.

(Later maybe some macros should be used for this?)